Apples get the job done. They're there to let you do what you want to do, and do it fast.
For typing letters, spreadsheets, internet, iTunes, all that kind of thing, the Mac Mini will suit your needs perfectly.
In general, Apple products are better than windows-based machines in every respect, except for the fact that far fewer games are made on Apples. If you aren't bothered about playing games on your computer (instead, why not play them on a PS2 or XBOX, where they often come out earlier anyway?), then go Apple.
Be prepared to give a week or two learning the new interface. It is very different in many ways than XP. In many of these ways its simpler, but it still takes getting used to.
As WoWo says, the main two cons of the Mini in particular are that 1) its small, so like a laptop, its more complex to upgrade yourself than a larger-sized desktop machine, and 2) its only for general use, not for intensive image processing or things like that. If you're planning on doing the latter and still want a Mac, get one that's designed to do that sort of thing, like a Powermac.