I've looked at this example from 2003 and converted it to something that compiles with qt4.7. Here: https://github.com/aewallin/sandbox/tree/master/qt_opengl_threads
Each window is a QGLWidget with its own QThread associated with it that does the drawing. That means the UI should stay responsive despite heavy processing in the threads.
I wonder if this can be made to work with libQGLViewer ?
(The screenshot has caught many windows in the middle of a drawing operation. I couldn't get double-buffering to work. In practice it looks very smooth to the eye.)
Apple seems to have a reasonable take on this:
http://developer.apple.com/library/mac/#documentation/graphicsimaging/conceptual/OpenGL-MacProgGuide/opengl_threading/opengl_threading.html