I’m really pleasantly suprised how well the desktop effects in Ubuntu Feisty work. They’re supposedly still pretty experimental, but the default compiz effects run just fine on my 4-year-old HP laptop with Mobile Radeon 9000 w/32 MB VRAM. And I’m using the open source ‘radeon’ driver. Obviously I’d get seriously better performance on a more powerful machine, but even on this old dog I’m enjoying a more pleasant experience with added depth on the desktop — the same reason OS X was and continues to be so cool. In addition to just simple 3D-depth, placing virtual desktops on the sides of cube considerably boosts their usability. It is now far easier to remember where something is when it has a physical place in space.
By default Ubuntu does not include a settings manager for the Desktop Effects, so I recommend installing gnome-compiz-manager (available in the Universe repository) or compiz-settings. The latter is less mature and more messy, although it doesn’t come close to the mess the Beryl settings manager is. I recommend the latter only if you want to try the compiz-extra plugins.