I thought the same in my previous comment, but after a bit of searching, the Like button is not optional at all.
It is capable of tracking both logged-in Facebook users and even users that don't have a Facebook account. It sets a cookie without you clicking it.
http://papers.ssrn.com/sol3/papers.cfm?abstract_id=1717563
Scenario: The web user does not have a Facebook account
...
after visiting a web site on which Facebook Connect has
been implemented, the request for the Like button
includes a cookie. This cookie has an expiration date two
years from the moment it was issued. However, by browsing
across web sites, additional cookies can be placed on the
user's computer and these can be added later on in new
requests.