The big downside of the moderation system on Slashdot is that you can’t both participate in a discussion and moderate at the same time. I want people who are interested and well informed on a subject doing both in the same discussion!

Meta-moderation was an interesting idea, though they seemed to have stopped promoting it much by the time I stopped posting there often. I’m not convinced it’s as effective as having a small pool of “super-moderators” who can not only affect the prioritisation/visibility but also comment themselves to guide contributors in positive directions, but practically speaking, it might be more scalable.