I suppose it depends what level of fan you are talking about. When I tell people that I got to meet and interview Dave Goelz (Gonzo, the Great) most of them think that's really cool and are excited. So, I think there's a lot of love and fondness for them, but it lurks under the surface. It's not as prominent or hot as Harry Potter or Twilight or maybe even Star Wars and I think that's because the Muppets haven't been out been out there as much.
I do know that when Muppet Boehemian Rhapsody was released on You-tube it became ENORMOUSLY popular almost immediately. I actually Dave Goelz about that and he said he didn't understand why, but he was happy.
So, I think they're out there... maybe not as fanatic as they once were, but still there.