I'm probably upgrading early, assuming I hear good things about it.
I'm a ColdFusion developer, and I'd like to install a development copy on my MP. ColdFusion and Macs have an awkward history:
ColdFusion 7 worked with OS X 10.3.
OS X 10.4 came out, and ColdFusion stopped working with it.
Now ColdFusion 8 is out, and it works with OS X 10.4.
So what happens when OS X 10.5 comes out, is anybody's guess.
Because of the potential conflict, I feel more comfortable having my final OS in place THEN installing ColdFusion, than getting ColdFusion up and running, then upgrading the OS. I don't know why. I just have a gut feeling that undoing any problems ColdFusion creates will be easier this way.