The new Metacity compositor in 2.21.5 is pretty sweet. It has only very simple effects (no eye-straining wobbly bullshit or workspace transition effects that just waste time), so it isn’t nearly as annoying as Compiz demos make compositing seem to be. It also made the desktop feel a little faster. The new desktop switcher is also a good deal nicer than the old one. Once an exposé-like feature is added, I think I’ll be all set with Metacity. All in all, I like it quite a bit.
Hopefully Ubuntu replaces the “low-bling desktop effects” option in the desktop effects setup with the new metacity. Compiz is a beast and it can’t even work on common setups like any machine that doesn’t support accelerated GL.
The only “bug” I’ve noticed with the new compositor is that windows sometimes get drawn to the screen before they have any content, so you see a very short flash of garbled pixel data. I’m not entirely sure if that’s a problem with Metacity, with X, or with GTK+. It’s not really critical, and I imagine it’ll be fixed in whichever layer needs it soon.