Facebook is not exactly well-known for being a paragon of privacy protection, and now their 'Like' button is drawing scrutiny from privacy watchdogs. The Like button uses an iframe, so Facebook can track Facebook users via your website, whether they're logged in or not, and whether they actively click the Like button or not.
Facebook claims that the tracking data is anonymized, is not shared with 3rd parties, and will not result in contextually matched advertising.
Given Facebook's reputation, do you believe that Facebook really intends to keep Like-button data completely anonymous, or do you assume this privacy policy is likely to change in the future? If there is any potential for privacy violations, are webmasters complicit for adding 'Like' buttons? What if you're in a discretion-related market like Ashley Madison or sell personal products like feminine hygiene -- do you worry about Facebook tracking your customers via a Like button? Is this an ethical dilema for some webmasters, or is it a non-issue?