Somehow since LION is installed on my iMac 27" 2010-model I get maybe once every 3 hours a black screen. On the main screen and also on the attached 24" ACD at the same time. For one or two seconds. Looks like sleeping but actually I'm active with mouse and keyboard. Not sure if linked to LION or iMac issue; but as LION came later I guess it might be linked to that one ? Anyone with similar experience ?