I normally run Firefox with the "NoScript" add-on, which prevents any web content from executing unless I give it permission to do so, and I don't get the Facebook button at all. If you're concerned about online privacy, you should definitely be running NoScript, or something like it.
“online privacy”
Oxymoron.
I am VERY concerned.
This cartoonist had an FB page which was hacked. All of her “friends” were contacted and threatened.
She’s now in the witness protection program.
http://www.realclearpolitics.com/articles/2010/10/05/the_molly_norris_precedent.html
A U.S. Cartoonist in Hiding: The Molly Norris Precedent