A lot has been said on Meta over the past couple of months about problems with the review queues; just have a look through the review-abuse tag. According to one common theory, many of the worst individual reviews are submitted by users who are just trying to grind out the Reviewer and Steward badges.
These users completely ignore the intended purpose of the queues — or so the theory goes — and instead press whatever buttons allow them to increment their "reviews done" counters most quickly. That translates into a lot of upvotes/accept votes on terrible new user posts/suggested edits.
If the theory is correct, bad reviewers should stop reviewing as soon as they hit a thousand total reviews and get the shiny gold Steward badge, because additional work after that point would lead to no additional reward. Well, even considering the 20-review-per-day cap, those badge grinders have had more than enough time to get their virtual pieces of gold.
I'd like to put the theory to the test. Has the number of bad reviews per day decreased recently? How about the proportion of bad reviews to total reviews? Ideas for how to measure these values are welcome.