sometimes when I start my AppleTV from sleep it does not bring out any video signal. The tv-screen stays black. It happens nearly half the time. The sound is no problem - I can hear the menu-sounds. In that case I have to pull the power-plug and restart the ATV. Doing a warm-reset by pressing menu and play does not solve the problem in most cases.
It is a ATV2 with the recent ATV-flash. The problem was there since ATV 1.4 I think.