After opening it you get a dialog that lets you configure a backup plan. A plan specifies the list of the items to back up, the backing up interval and the destination for the copy (be it a remote server, your iDisk, a local volume or a CD/DVD). Setting up the items to copy is trivial because the program offers you a set of predefined plan templates: copy personal settings, iLife data, purchased music or the whole home directory. Of course, you can configure these in a more fine-grained fashion, specifying whether your keychain, your bookmarks, your calendars, your photos, etc. should be copied or not.
A few clicks later, the plan is created and the program will automatically take care to issue the backups at the predefined intervals. Related to this, here is one thing that is very useful: if the computer was off at the exact time the backup should have run, it will do the copy when it becomes on again. I wish cron(8) could do something similar, because desktop PCs are not up the whole day (I know there is anacron, but it'd be nice if the regular utility supported something similar).
Unfortunately, the Backup utility is tied to .Mac. If you do not have a full account you are limited to 100MB per copy. And while the iDisk and this backup facility is very nice, I don't find it worth the money.
What I'm now thinking is that having a similar free utility could be very nice. It'd perfectly fit GNOME in the name of usability! It'd be even nicer if it'd run in the background, detached from any graphical interface (so that you'd set it up and forget in a dedicated server). Hmm... looks like an interesting project; pity I don't have time for it anytime soon (too much long-overdue stuff to do). Wondering if something like this already exists...