I'll be getting a 6800GT because in most of the bench marks it performs as well or better than the X800 Pro. It only falls behind when AF is on high and I think that that's a driver issue that will be fixed. I also think that whatever happens with SM3.0, when the performance and price between the two cards is so close, why not go for the card that has it? That way I don't have to worry about it in the future and there's a good chance the card will last longer. It also seems to overclock really well so, in six months or a year if and when it starts to show its age, I can look forward to a healthy boost in performance. So again, it seems more future proof than the X800 Pro.
And, though I wouldn't be saying this if there was a clear winner, I want to support the company that lost last round and that's Nvidia. If one or the other company begins to dominate the other, that's no good for us, the consumer. In other words, I don't want ATI to think they don't need to continue pushing the envelope and though the X800 line is undeniably powerful, its architecture, as I understand it, hardly innovates beyond their last line so I'd like to reward Nvidia for coming up with something new.
Really though, you can't go wrong with either card and so you can afford to be picky and even illogical in your reasoning.