"What I'm having a hard time with is it's the same questions over and over and over again, and it's the same guests. Some of them, you know, the inside voice is 'wow, you're still working?'" she told Letterman. "I thought, you're going to be a talk show host, you just talk, how easy is this gig? Until you realize some [guests] are better at acting, some people are better at a script."
"That's right, they really shouldn't be on a talk show," Letterman agreed. "The other problem is when they say 'Oh, Dave can ask me anything.' Then you know you're in trouble because 'I may not be all that curious about you.' What am I going to say?"
He joked that it's even harder to come up with questions for a boring guest now that he's quit drinking.
"I have new questions, like 'when was the last time you've eaten a pear,'" she said.
DeGeneres also said she's not sure what to ask this season's first guest.
"Hillary Clinton is our first guest ... but I'm not into politics. It's either going to be interesting, confusing or really boring. I have no idea what to ask her at all because I really don't know politics," she said.
This season of the show will kick off in New York, so DeGeneres suggested she and Letterman get to know each other better.
"Could we hang out sometime?" she said. "We have so much in common. I know you don't do a lot, I don't do a lot…"
"And we both like girls," quipped Letterman to the openly gay comedian.
The new season of "Ellen" premieres on Sept. 4.