Snapdragon, Xenon, slimmer, less bugs at launch, Compass, Trackball, better email client. Not sure whether I prefer Cap or Res screen, but I wouldn't change the resolution or colour depth.
Until then, I think I'll hold off on the N900 - the device doesn't seem to know which market it's aiming for, and also Nokia's silly insistence that the N900 is the 4th step of 5, and that it's a web device not a smartphone, is making people think that Maemo 5 is just a temporary stepping stone.