Thumb is an application that can best be described as a slightly simpler Hot or Not for just about anything.
The premise is simple: if you're rating content submitted by other users, you give a thumbs up or down (or neutral). If you feel the need to comment, you can; the comment will be accessible only by the poster of the question.
If you're asking for something to be reviewed, you can either take a new picture or choose from your existing library. Within ten minutes of posting, you'll have nearly 50 responses.
Honestly, this is something I never thought could be fun, but if you're looking to waste some time and see all sorts of randomness, or you want real advice on whether you can get a nail near a sidewall patched, there are a lot of neat things you can do with Thumb.
It does suffer a bit in the messaging section, as when you get a ton of replies there's no way to easily mark all of them read, but hopefully this will be fixed in a later release.
Thumb is free, contains no advertising that I can find, and is known to be highly addictive.