I've been holding off upgrading until Doom3/HL2 came out. I think now (or maybe a month down the road) is a perfect time for an upgrade. It looks like today's high end systems will run doom3 perfectly, meaning they should also be capable of running new games for the next 1-2+ years. I think i'm going to wait a bit longer for Video card price drops and finally upgrade!
Sh!tty thing for me is that I have absoultely no parts that can be recycled from my current computer, too out of date, so I have to build from scratch.