Comment 2 for bug 436496

The high X cpu usage is probably just a symptom, not an indication of a bug in X itself.

X is a server and responds to requests from client applications. If the client app is broken, it might make X requests too rapidly, which bogs down the X server (well, at least it doesn't crash!) In such cases the bug is really in the client application. For assistance in troubleshooting issues with high CPU loads for X, see this troubleshooting guide: http://wiki.ubuntu.com/X/Troubleshooting/HighCPU