I did a clean install on my G5 and I have run into quite a few problems.
First, programs at times don't allow new windows to show up. For instance in Safari if you use command N you see your window pop up when right clicking on the dock icon, but you never see it on your desktop. Only a logout / login works to fix it.
Second, preview is messed up, it crashes, it runs worse, and it sometimes loses the borders and only shows the photo in the middle of the screen.
Third, finder is buggy at times, when clicking on folders it sometiems gets messed up and even a re-launch doesn't fix it. I have to restart.
To say the least, I can't go more than 7 or 8 days without having to do a restart. On panther I went 121 strait without a re-boot. I think tiger was rushed. Overall, I am not a happy camper. It doesn't run nearly as fast as Steve showed it at the demo's. I even have a dual 2ghz g5.