I wasn't surprised that Apple announced revisions to the iMac line, having seen some clearance sale adverts from Apple resellers in the last week or so.

Apple probably didn't warn its resellers, but they have become accustomed to reading the entrails of stock figures and delivery times.

Anyway, faster processors, memory and graphics are nothing unusual in a 'speed bump' update like this. For most customers, support for SDXC memory cards is probably a 'future proofing' move as they don't yet own a digital video or still camera that support these extra-high capacity cards.

64GB SDXC cards currently sell for around $A300 - expensive, but about half the price of a similar amount of memory in the form of multiple 4GB SDHC cards. According to Panasonic, a 64GB card can store around 8.5 hours of HD video at maximum quality.

Some people are probably getting excited about the Mac Pro refresh that offers various CPU combinations from a single 2.8GHz quad-core Xeon to dual 2.93GHz six-core Xeons (prices start at $A3499), or the 27in LED Cinema display (2560 x 144 pixels, iSight, microphone, speakers, powered USB hub and integrated MagSafe charger, shipping in September).

But to me, the most interesting part of Apple's announcement was the $A99 Magic Trackpad, an external version of the multi-touch trackpad that's been part of the MacBook family for some time. I've been expecting an equivalent for desktop models ever since multi-touch arrived. I'll have more to say about it when (if?) I have a chance to test one.

Apple's latest quarterly results included record revenue of $US15.7 billion, and profit of $US3.25 billion (up from $US1.83 billion for the year-ago quarter).

Behind these numbers were record Mac sales - 3.47 million units - which is possibly one of the reasons why chief operating officer Tim Cook said it was too early to tell whether customers are substituting the iPad for other products in Apple's range.

Some analysts are suggesting a halo effect from the iPad is helping to drive Mac sales, but I'm sceptical. Continuing concerns about the economy in various parts of the world makes it harder to imagine people buying iPads and then rushing out a few weeks later to buy a Mac. I'm not saying it doesn't happen, just not often enough to drive record Mac sales.

According to chief financial officer Peter Oppenheimer, Mac sales to education customers were at record levels, and I just can't see room for a halo effect there.

And Mac sales grew particularly strongly in Asia Pacific - most notably in China, Korea and Hong Kong - but Australia was the only country in the region where the iPad was launched during the quarter (and it was only on sale here for about a month).

I'm going along with Cook in saying it's too early to tell whether cannibalisation will occur, but I am sceptical.

The iPad is designed to be an adjunct to a computer, not a completely standalone device. So I'd suggest that there is certainly room for a halo effect (it's not hard to imagine a proportion of those record Mac sales going to people whose first Apple product was an iPod or iPhone, and the same could happen with iPad buyers), but if cannibalisation does occur, it will be to the extent that buying an iPad delays buying a new computer for budgetary reasons rather than killing off the need to buy a first or replacement computer altogether.

In fact, I'd argue that if an iPad completely meets your computing needs, you probably wouldn't have purchased a conventional computer at all.

One of the significant features of Safari 5 is its provision for third-party extensions that add or change functionality. We know Apple is planning a gallery of selected extensions, but not what the criteria for inclusion will be other than "an innovative user experience".

I'm not totally convinced. The browser I currently use most is Camino (Safari isn't completely compatible with an online application that I have to use), which doesn't have extensions and I can't say I miss them.

I've only been inclined to install a few Firefox extensions, and I could live without them. For example, AutoPager automatically loads follow-on pages (eg, from Google or news sites that split articles across multiple pages), and iViewFox is the most convenient tool I've found so far to download ABC programs for offline viewing. Both are handy, but not essential.

I know NoScript has a lot of fans, but given my limited use of Firefox I'm not sure that it's worth bothering with. If there was an equivalent for Safari or Camino, I'd probably install it - so if you know of one, please leave a comment.

Anyway, I won't be rushing out to load up Safari with dozens of extensions - will you?

One of the best things about Time Machine is that it does seem to have made less-technical Mac users pay attention to backing up their computers. They can spend around $100 on a 1TB external drive, plug it it, and let Time Machine take over. From there on, no intervention is usually needed.

The next best thing about Time Machine is that it makes it possible to recover any of several different versions of a lost or damaged file. The way Time Machine consolidates backups over time (hourly to daily, daily to weekly), so there's no guarantee that you'll be able to recover a file as it was at a specific point in time. And the quicker you delete a file after creating it, the sooner Time Machine will drop it from the backup.

Another issue is that Time Machine is very inefficient when it comes to backing up very large files such as databases or virtual machine images. The slightest change means the file must be backed up in its entirety, and that can fill your backup drive very quickly.

For example, if you have a 4GB Entourage database that gets backed up every hour, that can occupy 80GB or more for today's and yesterday's copies, then another 4G per day for the previous month. That's a running total of 400G before we reach the older weekly backups.

A 4GB virtual machine image could take up the same amount of space (assuming you have an application running all day, every day), which means your backup disk is going to be full in about a month.

Another issue revolves around how quickly you need to be able to recover from a major problem. While you can restore from Time Machine as part of the Mac OS X reinstallation process (eg, after replacing a failed hard disk), that's still a time consuming process.

If you had cloned your hard disk to an external drive, you could immediately boot from the clone and carry on working until you have time to replace the internal drive and reclone it.

But cloning isn't really a backup strategy, as it only provides very limited protection against issues like inadvertently deleting a file. Once you've cloned the drive for the day, the previous clone has gone.

And in the event of a serious incident such as a fire, you probably won't have time to remove your clone or Time Machine drives from the premises. That's when a remote backup system comes into its own.

My current strategy uses Time Machine to back up most of my data. The main exceptions are my Entourage database (copied nightly to an external drive via Apple's Backup utility, keeping around two weeks of backups), and media files such as podcasts and recorded TV shows (which I don't back up at all).

My work in progress and certain other important files are also backed up to MobileMe once a day, and I do an incremental backup of my iPhoto library to CD or DVD (using Backup) every time I import a batch of photos. (I really must get in the habit of sending additional copies on optical media to a relative for safe keeping.)

Remote backup isn't a complete answer for Australian users, largely due to the relatively slow connection speeds (roll on the NBN) and the tendency of ISPs to meter uploads as well as downloads.

Why don't I clone my hard drive? If my main computer fails, there are others that I can fall back on until it's ready for use again.

What's your backup strategy?

This isn't a Mac-specific story, but it is highly relevant to Mac users that have found they can't rely 100% on Preview's ability to display PDF files.

Adobe has already released the security updates for Reader and Acrobat that were scheduled to appear on July 13. The company's quarterly release schedule that would normally fall on the second Tuesday of every third month, in part to align with Microsoft's monthly schedule.

But Adobe has made it clear that the quarterly schedule will be ignored when it's necessary to provide protection against real-world threats. And that's what apparently happened this time.

One of the fixes in Reader and Acrobat blocks by default attempts to launch executables or other harmful objects contained in a PDF file. Back in March, a security researcher showed how the text of a warning dialog could be modified to encourage users to allow their launch, and Adobe has also changed that dialog to make it harder to trick users.

Another mirrors a recent change to Flash to remove a vulnerability that might allow an attacker to take control of a system.

So if you haven't already updated to Reader or Acrobat 9.3.3 (or 8.2.3 if you've had to stay with the old major version for some reason), it's probably worth doing so.