If you get an apple get the extended warranty, they break all the time. (go ahead start flaming) We have a large selection of apple crap here and without the extended warranty you end up with paperweights very quickly.
Personally I have a toshiba and a dell. I like them but I hardly use them. And yes viruses can happen. But you usually have to do something stupid to begin with. So don't do anything stupid. Yes run a good antivrus. But I can fix a system with a virus. Try to remove the power supply in a g5
(for those who don't know. Remove the cover, remove the processors (you need a special 8" p1 screwdriver, which apple won't sell you, and a special 8" hex which oddly you can pick up but you usually don't have on hand), remove the board, say a magical spell, and the power supply comes out(we hope), bitch because it all doesn't go back together again and fling it from a rooftop)
The application situation did get better since it is all freebsd now and ports does work to a certain extent. Networking works better but it isn't seemless yet.
So you can scream from the highest mountain that the registry will be the downfall of windows, and I might even be inclined to agree with you. But I can't recommend apple for reliability, I mean if you want reliability, and security go sparc with netbsd.