We have a guy that talks and talks and talks. He is extremely smart and knows his work and can talk about it forever. Just when you think he is done talking about work, he changes the topic to something completely irrelevant (like his son). He can then talk about that for hours and hours.
If you try to walk away, he will follow you down the hall! It's quite amazing really. If someone is cornered at their desk, we will "save them" by calling their phone and disrupting the conversation so that the guy leaves.
He is a nice guy though and gets his work done (hard to get your own work done though when he's talking your head off )