This problem is exclusive to unity (when running compiz with gnome-panel, this doesn't happen).
1. Close all windows opened, if any
2. Open a terminal and run 'top'
3. Notice that compiz is consuming a lot of CPU time (although there is nothing special running). In my case, it's consuming about 13% when idle.
4. Unmaximize the terminal window, if maximized, and start moving the window slowly
5. Notice that compiz is now consuming much more CPU than before (in my case, arround 50%).
6. Open a video.
7. Notice that compiz consume much more CPU than idle (about 25% in my case), although I'm not doing anything related to window management.
8. (optional) Install the gnome-panel package and choose "GNOME classic" in login screen. Start compiz with "compiz --replace" and follow the steps from 1 to 7. Notice that the CPU consuming is much lower (in my case, 1% when idle, 25% when moving the window and 9% with the video).
DistroRelease: Ubuntu 11.10
Package: unity 4.0.1-0ubuntu2 [modified: usr/bin/unity-preferences usr/share/applications/unity-preferences.desktop]
ProcVersionSignature: Ubuntu 3.0-2.3-generic 3.0.0-rc4
Uname: Linux 3.0-2-generic i686
Date: Thu Jun 30 11:54:20 2011
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Alpha i386 (20110610)
UpgradeStatus: No upgrade log present (probably fresh install)