I work on a Mac OS X
processor: 2 x 3.2 GHz Quad-Core Intel Xeon
Memory 16 gb 800 MHz DDr2 FB-DIMM
2 ATI Radeon HD 2600 XT
OpenGL interactive in previewing, nothing happens when turning it off.
AE CS4
It has happened with a single mov layer and in a project with about 200 layers.
I would describe the flicker as black frame drops at random places. Sometimes it happens while rendering and sometimes when previewing.