After over 20 hours of gameplay, I finally got my first CTD. I had been playing about four hours straight (damn this is addictive) and made it from level 1 to level 3. About halfway through level three, I decided to head back to a big vendor on level 1 who had something I wanted. When I started up a stairway back to level 2, I got a CTD. Wish I could be more detailed with this report, but there wasn't any further noticeable trigger other than walking into the stairwell, and the long stretch of play time.