The one-liner: the 50D looks like a fine camera.
The long version:
If Canon is planning a major coup with the 5D Mk-II, then they’re certainly not tipping their cards with the 50D. The 50D is a safe play, straight from the book, and that’s just Canon’s preferred way to play the game.
The 50D’s claim to fame is to have the potential to produce the most detailed images from an APS-C camera yet, and of course to undercut the D300 in price. The move to gapless micro-lenses should give it D300-level sensitivity with 25% more resolution at the end of the day. I have no doubt that Canon did a fabulous job with the sensor as they always do.
I conclude the 50D is the king of the most visible and most vocal market segment today, but for how long? The 50D’s weakness is that it’s not very innovative. It’ll be easy to displace it with something innovative.
Compared to the D300, the 50D is cheaper. Plainly. The value statement is about equal because the D300 is more camera for more money, given that you are willing to accept there are qualities in cameras that are not just image quality (it's the most important item but not the only item).
If the rumors about the D90 are true (i.e. that it shoots HD video through live-view) then I think the 50D is in trouble. Otherwise, I think it's on solid ground. We'll see very soon.