So we've had a mass retag on SFF. I don't know what the rate limit for retags is, I don't even know whether there is one (though I'd be surprised if there wasn't), but I'm pretty sure it's too high when a user can retag 50 posts in 40 minutes.
I don't know what the limit should be. Quite possibly it shouldn't be a plain limit on the number of retags: I'm far more confident in the quality of 20 retags intermeshed with 10 edits and 15 votes than in the quality of 20 retags straight.
The front page may also be a factor: if the front page is close to being just one user, maybe we should stop this user from editing until others have chimed in.
As usual, moderators should have higher limits, which is not to say none at all.