Facebook can be a huge productivity sink, but it doesnt have to be, it all depends how you use it. First time users (myself included) add all kinds of apps in an effort to get the most out of Facebook, which is fine until you start having so many friends that responding to all the requests for gifts, flirts and more events than there are days in the week become unwieldy. At that point its time to remove all the silly little sheep throwing, kiss blowing, entourage showing etc apps and begin using Facebook for the thing its best suited to.... staying in touch with friends and arranging mass gatherings (birthday parties for example).
I recently celebrated my 41st birthday and without Facebook I probably wouldn't have managed to get over 150 people together for the party, let alone let my 400+ other friends know my birthday was coming up. In a month or so when I move to Bangkok to start a new job I plan to have the mother of all leaving parties.... If I can I'll get all 500+ friends to my leaving party. Even if they don't all make it they will at least all know that after 35 years in Hong Kong I'm moving on and they'll still be able to reach me if they want to visit me in Bangkok.
Incidentally, this is 500 people I actually know well enough to call them friends and who are on Facebook. Question to Erik, if you lived in an apartment building for 10 years and had the same doorman for all that time, at what point would you consider him a friend ?