When it comes down to it, it seems people are making choices relating to their preferance (ATI vs nVidia).
Let me just say, I'm a strong supporter of nVidia (I use it, and always have) but I must say that I see the X1800XT beating the 7800GT and reasonably so. The X1800XT is like the next generation of cards.. and has double the memory.
The 7800GT is cheaper though, and does a wonderful job.. but, the X1800XT might perform better for a longer time.. (thinking for the future).