Like Bowser, I've built my own systems for some time now (an old post on how I built my current system can be found here. The bitch is bringing yourself up to speed with whatever the current processor/OS/bus/etc. tech is. Hardware, software, and especially driver compatibility has to be researched, especially with newer systems. Someone deciding to build a Vista 64 bit system better pack a lunch.

For this reason, I tend to keep myself about one rank behind the front lines in tech. Find the cutting edge, and see what's a step or two back from it. For example, I'm only now considering WinXP. I have to have something like a piece of current software actually stop working on an old computer before I'm tempted to do a major upgrade.

Note from the link above that my current box is going into its sixth year. Running 24/7. I only switch it off when I go on vacation.