After half a day of working on 3.8.13-030813-generic, got the "[drm:i915_hangcheck_hung]" again. At least it was sort-of recoverable, as I was able to log into another tty and backup i915_error_state (attached). Hope it helps someone for diagnosing the problem. When returning to tty7, Screen was still flackering whenever I moved the mouse, and it didn't seem to respond to any clicks, so I had to logout by CTRL+ALT+DEL and then I could log back in without problems.
After half a day of working on 3.8.13- 030813- generic, got the "[drm:i915_ hangcheck_ hung]" again. At least it was sort-of recoverable, as I was able to log into another tty and backup i915_error_state (attached). Hope it helps someone for diagnosing the problem. When returning to tty7, Screen was still flackering whenever I moved the mouse, and it didn't seem to respond to any clicks, so I had to logout by CTRL+ALT+DEL and then I could log back in without problems.