I had the same problem the other day...very strange. it froze after I took the pic. and i could not even turn the phone off.
I had to remove the battery and then it restarted.
My only conclusion, is I have none.. haha
but I was taking the picture in a dark room so maybe it was trying to process the pic. and the OS froze.???
I know I have enough memory in my 2G card.