OK, got some clarification from 7thElement: he says it is not the total number of posts on the board, but the total number of posts by that member which affects it. That seems rather different from what Darker said, but I'll go with it because 7th is the man with the scripts.
Name changes cause a lot of load IF the user has a high post count because the mysql query searches the whole database (currently 700 MB) for posts and changes the username (the username is stored with every post)
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