Letterman's show used to be hilarious a long time ago. I remember the skits with Chris Elliott (remember the panicky guy and the guy under the seats - were they same?), and Brother Theodore was funny too.
That was a very long time ago. I haven't watched that show in years.
Last time I watched it he had these women parade out in tutus with steel belts on which they buzzed metal grinders that threw off a lot of sparks. It was supposed to be funny. That was about 4 years ago.