dunno if you letterman appreciators saw this, but i found this to be a pretty fascinating look in to the joke-writing process... including internal politics of the show:
http://www.vulture.com/2015/05/23-lo...letterman.html
actually i forget if this is the same article where some of them talk about being professional joke writers who fax in jokes all season long and maybe one gets used every two weeks or so and they make $50 for it. a labor of love and the thrill of seeing a famous person doing your joke on TV...