@OVK, @user/zero
I also experienced this this graphics issue on my N9 once in 2-3 months. Just SSH-ing and killing all meegotouchhome(they are automatically restarted by the watchdog) fixes this for me.
The other two issues that make me reboot my device are:
- updates stop being performed, and there is hanging process pkgmngr. I found recently that can be solved by killing /usr/bin/osa --packages as suggested by TMO user ginngs.
- swap memory runs low, and swappoff/on commands do not free it. Still no solution to this for me.