or the potential evil of the Facebook Like Button.
Even if you do want all of your friends on Facebook (your ex-boss, the people you went to school with) to know that you like to spend your day at work randomly visiting websites like
www.techcrunch.com and lets, for argument's sake, say that you do...
Whats to stop FB or other less scrupulous organisations mining that information for the next generation of direct mailing? As it stands, unless you opt out, direct mailers can get your contact info from the electoral register or from marketing lists 'shared' by companies you have signed up to. The data that FB has tells people what you like and how many of your friends like it so direct marketers can target you according to your preferences. Woo hoo more stuff to buy!
What about the Data Protection Act you might say? FB owns your data people. And it is subject to the privacy laws of the country it's stored in which means the Patriot Act is gonna get you...
http://mashable.com/2010/04/21/facebook-open-graph/