What you may not know
Time Machine seems to work only with external hard drives attached directly to your Mac, and other Macs running Leopard. But you can't use any old remote server, and you can't attach Time Machine to your AirPort Extreme's shared volume, either. And be sure to schedule some time for Time Machine - that initial backup of all of your files is a killer.
One of our favorite Time Machine features is actually apparent in the Leopard installation process: one of the offers in the Migration Assistant interface is to reinstall the contents of a Time Machine backup. In other words, it's easy to put your drive back together from a Time Machine backup, so you can get back up and running in the event of a catastrophic crash.
And while most demos of Time Machine are focused on the Finder, it's important to note that applications can be made Time Machine-savvy as well. iPhoto, for example, works with Time Machine: when you click on the Time Machine icon while in iPhoto, you'll be presented with a 3D interface into the history of your iPhoto library. You can fly back in time, scroll through the library until you found a mistakenly deleted photo, and then restore it to your present-day iPhoto library.
What we think
In our initial testing, Time Machine seemed to work quite well. After we finished our initial backup, we didn't notice any slowdowns in the typical usage of our machine due to Time Machine's background backup operations.
As a user, you don't have a ton of control over exactly how Time Machine operates. You can disable it, and specify certain locations that you do not wish to back up, but that's about all. One thing you will want to be sure of, though, is that you have a nice, large external (or internal) hard drive available for Time Machine - the more drive space you have available, the more versions of things you can keep. With a sufficiently large hard drive, you should be able to keep an extensive historical backup of your machine, enabling you to retrieve just about any form of any document you've modified.
Time Machine is perfect for nearly everyone - the only caveat being you will need a good amount of drive space to get the best out of it. Time Machine is not just for those who have accidentally deleted a file or lost work due to a hard drive crash. With its ability to store past versions of documents, it's also a great fit for anyone who needs to keep an audit trail, showing the iterations of a document from rough draft to final form.
One thing to keep in mind about Time Machine, however, is that the process isn't necessarily instantaneous. So if you create a file and then delete it a few seconds later, Time Machine won't have created a backup copy of that file. (While Leopard takes hourly snapshots of your drive, at the end of the day it collapses them into a single view for the entire day, so at that point your Time Machine backup is only good for tracking day-by-day changes.)
Still, version control is not really what Time Machine is for; instead, think of it as a really good insurance policy for all those priceless digital images, music, and documents that you store on your machine.
If you've got the drive space available - and seriously, go out and buy a big hard drive at the same time that you buy Leopard - Time Machine is a great idea that's been implemented quite well in Leopard. Yes, the cosmic 3D interface may be a little cheesy - but the basic technology works quite well.