I use birthdays as an occasion to de-friend people I don't know very well on Facebook.
The BlackBerry sends a little reminder that says "Today's Birthdays" (it's probably on the bigscreen version too, but it's not very noticeable) along with a list.
I look at the names and figure: if I don't know this person well enough to wish them a happy birthday (and by that, I mean, celebrate the idea that they were born), then I have no business being "friends" with them.
I also figure that on their birthday, they're getting so many facebook messages from their so-called real friends (most of which just say "happy birthday"), they will never miss me from the lineup if I disappear at that moment.
You can always "hide" the people on facebook that are too chatty, or who try to sell stuff via their status updates (apparently a lot of people use the "hide" feature to ignore relatives they don't want to hear from), but I prefer nice clean breaks.