I like it if everyone has some tension breaking aspect to their roleplay, and silliness tends to do that. It can take over the scene and steal the spotlight a bit, but that's a separate issue, I've seen more spotlight hogging maudlin clowns than the more traditional sort. That said, there are other types of humor and comedy than silliness, so I'd get bored of someone who only went for the one type of comedy as much as if they never went for any type.

To be fair though, I'm strongly biased against games with a solemn tone, and get bored with that sort of thing within a couple months, so I doubt I'm representative of the average gamer.