Yes, it's no fun when a Mac goes down... Usually they're quite reliable, but judging from various Mac websites and forums, weird things do happen.
I work in higher ed as an IT Consultant, currently responsible for about 100 Macs (eMacs, G4/533DPs, iMac G5s and Intel iMac 20"s). I began this job in '98 running a room full of 8500s! Here's what I've seen over the years:
The 17" AppleVision monitors accompanying the 8500s died like flies (bad video boards). Out of 13 eMacs, 2 or 3 went bad quickly (no video). The G4s have been pretty good, with a couple of power supplies and some IBM DeathStar hard drives dying. Oh, and several of the 17" Apple flat monitors have gone dark on the bottom half and then need a part replaced. Now I'm seeing the folding support legs going weak on two of them.
I have a similar model G4 tower at home (gotten used from another school) and yet another (bought on ebay). The school one is fine; the ebay one lost its power supply after I unplugged it to clean it but I replaced it successfully.
We bought 22 17" iMac G5s for a lab on special knowing about the bulging capacitor issue. I've had a few of these go down for various reasons, but now i've got at least 2 dead with bulging capacitors (I saw them with my own eyes). Now I await the demise of the rest. I stick eMacs in their place while we await AppleCare service.
Of our 47 new 20" Intel iMacs, only one was bad out of the box--it wouldn't accept a disk image (in restore mode), nor could I insert a DVD into the slot to boot from it! We got that one replaced. The rest have made it almost through a semester intact. (BTW, you can't get into these like you can the G5 iMacs).
I've also seen other people's PowerBook G4s exhibit the half-black screen and white spots (including one owned by a student who worked at an Apple Store!).
So, yes, it does seem quality has gone down in more recent models, as compared to the older beasts (the beige G3s just don't die, do they?). I now have a 2-month old MacBook and have had no trouble at all--so far!
Do buy AppleCare!
PS: I'm writing you from a PowerBook G4/667 I got used in a trade. Never had a problem with this one over the past year I've had it... Everything works.