I have exactly the same problem as Myrdain. Sometimes the game freezes completely, sometimes the character keeps running, audio continues, waterfalls still fall etc, but the only thing I can do is open the task manager and end the process.
I've been through pretty much all the posts describing this type of problem, been through the first aid threads too. Uninstalled old drivers, AMD dual core optimization patch, all that jazz, but no luck. Sometimes it runs for half an hour without freezing, other times about 30 seconds. I have noticed oddly enough that it seems to run longer when the graphics are turned UP, but that might just be coincidence. I have the STEAM version, so unfortunately I can't try any of the hotfix patches.
Sorry to post this in someone elses thread, but I thought considering it was the same problem for both of us, a bump and a bit more attention couldn't hurt to solve our problems!