I just checked, and I'm very surprised that all my wheels are rolling. I don't think I want to see what's in there until I have a problem.
Just recently had the "fun" of pulling hair/threads off the vacuum rollers. Enough of that sort of thing for now! Have you ever noticed the threads caught on the wheels of shopping carts at Jo-anns? I should sneak a picture some time because they're kind of amazing and funny.