I was in the same boat as you, but I was pondering getting a PM G5. I decided that a new OS wasn't going to fix the issue that my G3 B&W wasn't able to edit photos fast enough, quickly edit videos, or run audio conversions in a timely fasion. I needed a faster computer, and Tiger wasn't going to do THAT much to make me wait to upgrade hardware.
I know many on here are waiting to upgrade so they can get a system preloaded with 10.3, and come with CD's for 10.4 . Since software that will run on 10.3 should work fine on 10.4, I don't see the need to have redundant OS's. Unless you are talking Clasic and OSX there is little point.
If you need a newer, faster computer, get it. Waiting for what is faster, and newer does not make sence. There will always be something faster, newer and with more cutting edge software then your computer.