I have been noticing quite a number of "test" questions and answers being thrown into the mix. When did this start and what is being done with the information obtained?
There have been some complaints elsewhere (er, SO) that certain Reviewers are just clicking buttons as fast as they can just to get badges or to whittle down the queues. Because of this, they started throwing speed-bumps into the mix in the form of already-reviewed questions (and mod-hammered ones if I'm remembering right) to cross-check Reviewers against community standards.
If you get enough Fails, you're locked out of Review for a while
The details are found here: Why was I told, "Congratulations, this was only a test" when reviewing?
They've only recently added these to SF and SU, so they're definitely still tweaking the system.