I've been at this for awhile now and have discovered there's no point in waiting. Your best bet is to just get the best stuff for the money and try to keep it all semi-future proof (P35 chipset for example).
There will always be something around the corner. Wait for G71, wait for the x1950, wait for G80...don't buy now, R600 is coming in a few months! Now waiting for G9x series.
I'd say now is a great time as current hardware is decently powerful and DDR2 prices are low. (for example once Penryn/Barcelona/Phenom come out they will be **** good but it won't make C2D obsolete, C2D will be in the game for awhile as they are VERY capable processors, **** AMDx2 is still holding its own)