Tilt function/Orientation not working

I have a 64GB ipod touch 3G . I have recently upgraded the software on it to ios 5.1. Ever since I have notice the ipod has frozen twice and rebooted itself randomly while playing music. (Only twice though).

The tilt function, when watching videos does not seem to work at all anymore. It was working to start with , then it stopped so I rebooted the unit which caused it work fine again. Now no matter if I reboot it or not the tilt function does not work.

Any ideas?