As today's cards seem to keep a list of render commands and flush only on a call to glFlush or glFinish, is double buffering really needed any more? An OpenGL game I am developing on Linux (ATI Mobility radeon card) with SDL/OpenGL actually flickers less when SDL_GL_swapbuffers() is replaced by glFinish() and with SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER,0) in the init code. Is this a particular case of my card or are such things likely on all cards?
EDIT: I've discovered that the cause for this is KWin. It appears that as datenwolf said, compositing without sync was the cause. When I switched off KWin compositing, the game works fine without ANY source code patches