I singled out, and deleted my account from, Facebook because of one of the recent news stories that showed that they actively tried to build profiles of people that their users know who are NOT on Facebook. It's one thing for me to voluntarily hand over information about myself, but it's quite another for Facebook to sneakily try to access information about my contacts.

Does it make any practical difference? I'm not sure. Being totally invisible to surveillance may be next to impossible, but I found that action on the part of Facebook to be needlessly over the top.