Or, you could edit /usr/local/Library/Homebrew/utils/analytics.rb to send Google Analytics garbage (from random UUIDs) until Homebrew makes this feature opt-in.
Any rubyists want to provide a patch to do this?
use their opt-out if you want
Frankly I don't trust the opt-out code to be (and remain) bug-free. There are, as far as I can tell from searching, no tests. So I feel more comfortable maintaining a patched version with the calls nooped instead.