I'm actually asked this quite a bit, "how many systems do I have?", and "what do you use them for?"
Well, here's a list -
3 systems running windows xp - games, development, testing software, etc
1 AMD FX55 running Ubuntu - server development, databases, programming
1 FitPC running some flavor of linux - various network services, bots, etc
1 laptop running vista - dislike vista, used for software testing mostly, and checking my own sanity
1 mac book air - my system away from all my other systems, used for email, blogging, chatting, development, porting windows software, testing mac builds
There we have it, 7 computers in total running a mix of windows, linux, and mac software. Personally, I really like the Mac, even though it took some getting use to. I will admit the system was not the cheapest thing in the world, but I don't regret making the purchase either. To me, it was a perfect balance of computing horsepower, physical weight and size (portability is nice for roadtrips, etc), and I love the keyboard on that thing.
I could probably write a lot about the various "PC versus MAC" thing, but I'll save that for another time. I'll just say that both are nice for what I use them for.
I forgot to mention in my original post that I also have a couple "retired" systems that ran FreeBSD, NetBSD, slackware, and some other OS's... most of them are in pieces in the closets or recycled, literally, at the computer deconstruction place near downtown.