Now that I've upgraded to Unity 4.3 and 2D toolkit 2.3, I get more hangups in Unity upon shutdown than before. Since I'm only using 2D toolkit as additional asset, and the 2.2.3 version had similar hangup problems, I thought to drop the problem here as well...
The hangups mostly occur when I've tested my program in the Unity editor (using PLAY button) a couple of times and want to exit Unity. When doing so, nothing happens, other than Unity hanging itself up (not responding in taskmanager) and I have force-close it.