I am using Ubuntu 9.04.
Whenever I turn on Compiz while a OpenTK GL window is open (both in the examples and my own project) the CPU load for the thread's core goes to 100%. This makes the whole system very unresponsive.
Turning off Compiz (using metacity) the CPU drops to a few % and everything is smooth.
Haven't had this problem with any other OpenGL app/library.