Oddly, good Canon 5D image samples are appearing before good 50D samples. Anyway, despite the high rez, they are very impressive. The 1600 samples are smooth as a baby bottom. Which means that for general use, 1600 ISO can be the new standard setting for many photographers. Who'd have thought.
I know I’ve said it before, but: imagine what they could do with a 12MP full frame sensor. I'll bet it could gain a full stop over the 21MP one.
... It's true though that the 800 sample is sharper than the 1600 one (amazingly sharp actually). Perhaps it would be different if one turned off in-camera noise reduction, it often does a poor job.
By the way, talking about high resolution: I wish that some of the new super-sharp lenses that Canon and Nikon are bringing out would be slower and have stabilization. Sure, 2.8 is better than 4.0 all other things being equal, but all other things are never equal. A professional 2.8 zoom lens is very big, very heavy, and very expensive. 4.0 would make a lot more sense. And to release any new lenses at all without stabilization is just daft, so long as they don't even have any bodies with it built in.