Just a quick status update: we are taking this seriously, but don't want to jump to conclusions (or make rash changes unless they can be demonstrated to help).
As Geoff mentioned previously, we've fixed the bug whereby if two reviewers review the same item only one gets credit for it (realistically, this only affected some types of reviews, but editing was one of them so that's particularly bad).
Emmett has implemented some better analysis tooling for these queues, which should let us get a better idea of the scope and extent of the problem (once they're enabled).
update 2012-12-13
###update 2012-12-13 ManuallyManually suspending reviewing privileges has been introduced:
...for folks who fail multiple review audits in a short time...
update 2013-01-29
###update 2013-01-29 AutomaticAutomatic review suspension has been introduced:
...We're kicking blatant abusers out of the queues automatically now...