I installed Feisty recently after it went stable and I have a problem with the gnome panels.

When I enable the desktop effects, even when I haven't checked neither of the two options, just enabling them, my panels dissapear in all workspaces but the first. When I disable desktop effects everything's fine again.

My hardware is modern and Ubuntu recognizes it fine, particularly the video card. I have 1280x1024 and desktop effects when enabled worked fine and smoothly, except that this annoying side effect happens with the panels.

I believe I had the same trouble after my upgrade to 7.04. I think the default "Desktop Effects" is using compiz. I have always had trouble with this. When I installed Beryl and Emerald I am able to get all the efects to work.

Some of the effects do slow things down a bit on my machine. I am running on:
AMD Semperon 2400
Nvidia GeForce FX 5200
757 MB Ram