are you using the "Windows 7 Taskbar Progress Plugin"?
While I didn't actually see any freezing, I have noticed that when using this plugin, MC can become extremely slow to respond in some areas when left running for periods in excess of eight hours.
After removing the plugin, MC can now be left up three or four days without a performance hit.
If you are not using the plugin, I don't know what your issue might be. Something in auto import perhaps?
-marko