My experience, thus far...
So, I've had Leopard installed since last night. My first installation was just an upgrade; and when done, fired up and noticed some pretty HORRID animation relating to anything on the dock, including the genie effects, and oddly enough, the stacks (both the fan and gird view) seem to animate pretty smoothly, despite what I've heard about what others have said. Needless to say, I was severely dissapointed since I have the newest addition to the MBP line. Sporting the C2D, 2 gigs of ram, and a GeForce 8600gt, I would have imagined that this OS update would run far better than Tiger (which ran very well, by the way.) So I read up on the forums, and found out that many others were having the same problem with the upgrade, however I noticed many say that after an Erase and Install, it ran perfectly fine. So I decided to go ahead and give that a try. After backing up all my stuff, double checking, and all that prep stuff, I proceeded to install Leopard with the Erase and Install option. After installation was complete, I was still experiencing the sluggish animations... What is funny however, is that quick look, cover flow, the Time Machine and various other animations not related to the dock were very, very smooth; with one exception. Playing .mov's in coverflow/quicklook wasn't playing back particularly smooth either. And since I'm on the topic of Quicktime, I fired up both a 720p, and 1080p quicktime movie trailer from the apple site. The 720p one played back well, but the 1080p one had some noticable hitches.
Aside from the problems with Leopard, there are some things I really like about it too. Quick Look is great, Time Machine works well so far (obviously I haven't had much time to let it backup yet though), I like coverflow for some folders, the sidebar is much better, as well as networking, which finds other networked computers very easilly, and stacks are pretty cool too.
I could go on and on but that list will be too long. So there is a mix of good and bad, and I REALLY hope that Apple fixes this problem, I could be wrong but I think it might be related to the type of video cards; hopefully drivers will be updated to fix this.