I've been noticing that sometimes various sounds like notifications and dialer keypad tones will disappear. I don't have to reset, though--if i go to Settings->Sounds->Volumes, and move the volume sliders around, the sound comes back. Seems to be a bug with ICS, since it never happened with GB. Reminds me of Windows, where sometimes I'd lose sound, and would have to go into the Control Panel and mess around with the volume controls.