Thunderbird? Seriously dude thats back in '99.

I have yet to meet ONE person who outside of the office uses outlook/tb/anything who is also not a hacker. (iPhone/Android/etc does not count, and even on those they use the gmail app). Sure some use hotmail, some gmail, some migrating to gmail but overall gmail does a good job with this stuff.

The real advantage of facebook is that instead of YOU filling in personal info about your friends, your friends do that for you. And vuala, instant address book management.