I'm just going to echo what others have said:
If you need it or just want it now, get it now. If you can wait for a few months (ie, you have a backup machine), then wait. Personally, I couldn't live without a computer for more than a week.
I bought a G4 PB. The 12", it's the 867 MHZ with 640 RAM. I run Photoshop CS on it, Final Cut Express 2, Dreamweaver, word processor, etc. I'm very happy with it -- even in those larger apps. I don't play games, but I did try Halo and was a little disappointed. But, again, I'm on the older 12" unit. This little machine is just so portable that it makes up for any speed difference for me.
Do I want a faster computer? Yes, eventually. I'm saving up for a G5 desktop 😀 The little unit will be for portability, the big unit for the heavy graphics and other stuff.