This article in the Los Angeles Times [registration might be required] says that the network late night shows (Leno, Letterman, Nightline) are losing audience share to cable, and that they look highly vulnerable to further onslaught. This is probably so. I think both Jay and Dave have gotten too repetitive and predictable, and that audiences are starting to drift away. Whether the new shows coming into that market will be able to pick up those viewers remains to be seen. But if I were CBS, NBC or ABC, I'd be doing something about it.