I'm experiencing this: whenever y bring up the Dashboard, it is smooth. The ripple effect goes smooth, and displaying the "lower drawer" goes smoothly. Also, the scale-fade of the dashboard is smooth too. Always.
BUT...
If I dismiss the dashboard with the lower "drawer" open, the animation is jumpy, stuttering. This, on the other hand is happening to me since 10.4.3 (or more or less, I believe). I have been able to have the said animation running smooth in the past, and with only 512 MB RAM, which often caused a stuttering ripple effect; now my PowerBook is loaded with 1.25 GB.
I simply don't understand why does this happen.