The Composite extension, which is responsible for the eye-candy, is extremely unstable. It crashed twice for me while I was fiddling with transparency. The first time resulted in spectacular video corruption and complete loss of response to input; I had to do a remote login to bring the system down to single-user and then pound on the Magic SysRq key until I got a console. The second crash just kicked me out to a console. It's also slow as molasses, produces artifacts, the drop-shadow fade effect makes menus disappear, and occasionally all the windows except for the root window will vanish