I had the problem after about 6 months of MacBook Pro operation (MacBook Pro Mountain OSX 10.8.2).
On first start in the morning, the loudspeaker symbol in the command bar at the top of the screen was grey. System preferences Audio: everything was paralized. After restart, it was ok.
The problem always came back on first start of the day. At the end I performed a "Verify Disk Permissions" and "Repair Disk Permissions". There were 5 Permissions Problems. After repair, the audio was ok the next day first start.
If you run Permissions Repair: the Permissions are not repaired all at once. Run again Verify Disk Permissions, and Repair again.
Good luck.