The web intents javascript events do not leak personally identifiable information about the user who is visiting your site, as they’ve given no consent for you to have that information (that kind of information is available from the APIs we have that involve this kind of “agreement” via OAuth).
The information you get back is for you to identify the fact that it happened, and when, and on what DOM element and/or Follow Button on your page. Of course, if the account being followed is under your control, you could leverage User Streams to be streamed an event on each follow…