Letterman is my favorite by far, then Conan, then Kraig, and, finally Leno - no, wait!, then John Stewart, then Jimmy Kimmel, and THEN Leno!
(I don't like Leno - can you tell?
)
I don't think Letterman is necessarily going anywhere anytime soon, but I do think that he'srealizing there's more to life than work after things like his bypass surgery and shingles, and his priorities are changing a bit. I say good for him.
How Leno beats him in the ratings, I'll never know.