Amazing review here:
http://www.youtube.com/watch?v=VgTjSbpFDhQ
And this is why I will be upgrading:
1) Improved build quality (big deal to me!)
2) Larger screen
3) Tilting screen
4) More responsive screen
5) Much improved keyboard- I find the current one to be a bit tight. It was easier to type on the Mogul.
6) According to this video, improved battery life.
7) Damn its sexy!
Of course, I'll have to wait to get my hands on it to be sure...