I quit Facebook back in mid-May of 2010, it has not been a year yet, but it has been a significant amount of time. What I can tell you is that not a single relationship/friendship that I have has suffered because of it. There has yet to be a single instance where I regretted quitting Facebook.
I think that if a friendship suffers due to a lack of Facebook, it probably wasn’t a great relationship to begin with. Social media makes the art of relationships appear easy, while in actuality, it creates a false feeling of closeness that wouldn’t be there otherwise.
I’ve turned my account on and off several times, and late last week, started the process to delete it entirely[1. So the service says. I have doubts my files will be expunged from their servers any time soon.] after my uneasiness with the service grew too large to ignore.