I've had similar experiences, but never to the point where I'd have to restart the phone. Usually, if the camera cover doesn't activate the photo program, a depress of the shutter button might work, if not then go into the apps menu... and yes, by that time people lose their smiles :P

Alternatively, bring your Canon/Nikon SLR, put it on a tripod, stand at a distance and remote fire the camera with the n900 to show off Who cares if the camera doesn't work, you can control other cameras! muhahahahahahahahaha *cough* *cough* *cough* *splutter* *dies...*

Fred