A few more questions on this one.
Nicoloco - are you still not crashing with Fast Feedback off? If so, that is a really important clue. If you turn on Fast Feedback, can you recreate the issue with all models or just certain ones? It sounds like you were thinking it might be model related...
Tim - does turning off Fast Feedback in Preferences > OpenGL seem to fix your lock up as well?
Fast Feedback speeds up the drawing actions in your model (vs things like the speed at which you can orbit around) and only kicks in when performance degrades below a certain threshold. So Fast Feedback will only kick in when working on larger models. If you both are only seeing this issue with more complex models when Fast Feedback is enabled, that might be a further clue.
Also, we are wondering if you see a pattern in how many document windows you have open at the time of the crash. Or whether it seems to happen only with certain actions - e.g. only when adding geometry, or when selecting things etc...
Sorry for all the questions. We really appreciate your willingness to help us try to get to the bottom of this one.
Tricia