I watched my roommate spend over 2K for his computer then have to sink another few grand in constant replacement parts and it only worked about 1/2 the time in its 3 years, meanwhile my generic emachine, bought at walmart and upgraded ram/hd/videocard kept on going and going, till I replaced it with a Dell (because the processor type was too outdated), and even then the dell's run well. I've also talked to many other homebuilers who've also had all kinds of nightmares, although they still stand by their homebuilt pc choice.
So which would I go with in the future? I'd have to say buy a pre-built. I'd recommend just doing some homework, review what models you see on stores or the web, read the reviews (avoid ones with lousy ones) And look into what expansion capabilities it has (for add on vid card, ram, wifi, tv tuner, soundcard, etc)