> Anyway, I think aggressive moderation is a big part of Metafilter's secret sauce.

It's definitely part of the secret sauce, but I wouldn't call the moderation aggressive - it'd call it targeted to preserve culture. If MetaFilter has a first defence then it is the 5$ account wall, the second is the (almost legendary) snark, the third is the moderation. Moderation is almost always employed as a last resort, and it's rationale is normally documented.

The "secret sauce" of MetaFilter is really the community and everything else works to preserve that. The moderators of MetaFilter are the last resort in that process, but their are neither "aggressive" nor numerous, they are just very well chosen - not by algorithms, but by other existing moderators who actually understand the organisation/community they work in.