Well....
I haven't seen the Letterman performance yet. I'll watch it this evening (Tivo, y'know). However, I did watch Otto & George's YouTube video. (That's one ugly dummy). The jokes were not my cup of tea, but Otto & George are obviously crowd-pleasers when using the X-rated material.
There was a lot of criticism written about lip movement. Yeah, there was plenty of it. Apart from the style and content, the lip movement didn't really bother me, just as Edgar Bergen's lip movement doesn't bother me. (Actually, as a kid it bothered me, but for some reason as an adult, it doesn't). I'm not advocating that vents should flap their lips, but I don't think it's the overriding measurement of a vent performer's effectiveness. I think strength of character development in the figure is more important. And is the show truly entertaining?
Personally, I pride myself in my ability to speak without lip movement. But undoubtedly there are better performers out there whose lips move more than mine.