Sitting in any chair that is wet from anything is nasty, but warm and wet from a person is well over the top on the gross o meter. :)
I don't mind sitting in a chair warm from a person either, really, especially when it's a person I'm fond of. Whether the chair is damp from a person or a dog though, I'd just as soon not be sitting in it.
Any warm wet chair needs a smell test and a good cleaning.