It is strange, but it is as it is. I had about 20 ctd on thursday in 3 hours playtime, and not a single one yesterday on wednesday in 4 hours playtime.
I have a topic somewhere here on page 1xx i think ( lol ) but actually no real solution for this cause there are no real symptoms why it sometimes does it a day completly instable and the next day stable.
Try disabling AA, test windowd mode and reduce water multisampling to minimum, thats a half-way stable configuration for me.
The bugs people hit again exist for nearly about 6 years now, from oblivion, morrowind over fallout 3 and now new vegas (always the same engine a bit modified) - don′t expect to get it fixed fast - or even ever