This problem was first reported against GCstar, but it's not specific to that application.
Since they upgraded to Ubuntu 11.10, many users reported that the application is really slow. After some investigations, it appeared that the problem occurs when the application uses a background image. It was only reported for Ubuntu and doesn't seem to affect other distributions.
I managed to create a small script that shows this problem. Its only dependency is libgtk2-perl. After it's started, Xorg is using a lots of CPU and the whole system is less responsive. This script is attached to this report.