I do a mixture of buy my own and build, and have for at least 10 years, depending on what's en vogue, cutting edge, etc. I always stay away from bleeding edge because it's too darned expensive to depreciate that fast. Kinda like Toshiba HDDVD players.
Just built a new gaming rig on the Frys deal (E6750 with ECS mobo for $218), popped in 4GB of 1066DDR2 and a 640MB 8800GTS and all is good.
Total cost out of pocket less than $750 for a damned good machine.
Machine before that was a VAIO i bought in 2003. 3.4Ghz northwood (P4 HT), came with 1.0GB of DDRPC3200. I upped it to 2GB and replaced the FX5200 with a 6800GT that had me kicking butt on BF2 at 1920 x 1200 with max settings. With only that RAM & GPU upgrade, I was suprised that I got a good 4 years of gaming out of that thing with great performance, so would definitely buy another VAIO desktop with a Blu-ray burner.
The only thing I didn't like about that was the Non ATX proprietary power supply Sony used. I was still able to shoehorn another one in there, though.
I loved the modular nature of the Sony case, even if it wasn't the best at handling heat.
Computer before that was a custom built Athlon XP
Before that was a store bought Athlon 900.
etc etc.