Removes one bit of entropy from your identity, making it more difficult for sites to uniquely identify you.

I think the purpose is to show how easily some of these scare tactics can be defeated. This took what, 40 minutes to get posted? Less than an hour to thwart what is being hyped up as a big deal for anonymity.

As an aside, I think you should name it CoverAlls.

EDIT: I guess I worded that a bit harshly. Underpants is meant to be a PoC for a tactic that may work in some situations, but the feeling I got is that people are taking it to be a lot more serious than it is.