Or, even worse, there'd be a selection effect where the distribution of people who opt in is skewed from the total distribution of Homebrew users, ruining the dataset for any analysis one might want to do to it. There's a reason that Nielson Ratings collection isn't opt-in.
Funny, it's been quite a few years, but I remember being a Nielson family for a few months, and it was absolutely opt-in. We had to fill out a little booklet with what we were watching and data about ourselves.
