I've been using that for a while. It's, not so much surprising as interesting, how much it changes one's outlook.
It doesn't deal very well with the "Recent Comments" sidebar, I added a .5s delay to wait while the AJAX loads. That's not quite satisfactory, but I don't know how to tell a GreaseMonkey script to wait for a specific AJAX query to load.
EDIT: OK, now I know. It would be helpful if LessWrong could be upgraded to a more recent version of the Prototype framework.
A fun game you can play on LessWrong is to stop just as you are about to click "comment" and make a prediction for how much karma your comment will receive within the next week. This will provide some quick feedback about how well your karma predictors are working. This exercise will let you know if something is broken. A simpler version is to pick from these three distinct outcomes: Positive karma, 0 karma, negative karma.
What other predictors are this easy to test? Likely candidates match one or more of the following criteria: