Re: XServer hang (100% CPU)
Yes, this sounds like the X server bug. It occurs when the mouse crosses screens too many times while the X server is busy processing a request. In this case, the server was probably busy for so long because your system was swapping due to high memory usage.
The X server using a lot of memory is typically a sign that some application is requesting a large number of resources. You can check to see if applications are using a lot of pixmaps using the 'xrestop' tool.