Megarelix: I just did an experiment: loading a save from just after waking up with Tris, I was able to run for 20 minutes w/o problems. Then reloaded the save before facing the dragon on the brighe: the same. Then I loaded my most recent save in the Flotsam tavern: lasted about 16 seconds before CTD. In the next attempt I was able to leave the tavern only to crash outdoors after about three minutes - consistent with my average Flotsam experience.
The total of 40 minutes of pre-Flotsam play without problems does not seem like just luck. WIth MTBF of, say, 5 minutes, If crashes were just random, the chances for a successful run of that length would be about 1/exp(8), or 1 in 2500. This is a strong argument indicating the reason as either something Flotsam-related or some problem (memory leaks, corruption) developing with game time.
If I have time and patience, I may try to keep restarting until I can get to a place far from Flotsam and see what happens. Most probably, though, I'll just kiss goodbye, for the time being at least, to the $130 spent on the CE, get myself Honest Hearts and spend a few days with Fallout 3 NV. This is becoming more work than play.