I made that jump at the end of last year and discovered what worked and did not. Here is what I know:

1) MS Office will work fine EXCEPT Entourage. There is a bug in the database and it will take up all of your memory and cause you problems galore. I think I would crash regularly when using it. IF you do not use Entourage you will be fine. Otherwise you will need to wait for the new office that is supposed to be out soon. (I was beta testing it for a while, but decided to just ditch it for now.)

2) Intego NetBarrier & VPNtracker will not work on the same computer (Intel.) I use NetBarrier as my firewall and also to block ads on websites (ads on Tribe? I have never seen them.) Web pages look much nicer and cleaner. Unfortunately VPNtracker is something I need to connect to my multiple sites I support and it will cause a kernel panic as soon as I connect a tunnel. I have been without it for nearly a year now.

Those are the only problems I have had. There were a few other apps that just ran a bit slower because of the Rosetta process, but they work. Those two above are my major gotcha's. The problem with Entourage will be resolved with the new version. The problem with VPNtracker will be fixed with a new verison released after OS X 10.5.x