Having just installed debian6 19-04-2012 on to the sd card, everything seems to work, boots up, logs in, when startx is entered, the giant raspberry appears. Keyboard and mouse work fine, but the hdmi output seems to be cycling on/off, appears for approx 1 second, flashes off and then appears again.
The TV is a 9 month old Sony Bravia KDL40CX523 LCD HD 1080p TV, 40 inch.