If you’re a certain MIL you’ll use it to leave negating, dismissively rude and/or patronizing comments on your DIL’s status updates and pictures of the DIL and her family including her husband (your son), and update your status with thinly veiled attacks and passive aggressive insults.
After this goes on for about a year with DIL ignoring the behavior, DIL will get tired of every time she turns on the facebook app in her phone to update & check in with family & friends where they’re at in their month long traveling vacation far from home and share photos of the cool stuff they’re seeing and doing, DIL will get tired of seeing the steaming turds of malice you enjoy heaping on them and “unfriend” you so you won’t have to see her updates or be able to comment any more, since you apparently just can’t help yourself and be nice or say nothing at all, and while yeah, she should be able to ignore it another year and then another year until either she dies or you do, it’s really just such a smack in the face every time and it bothers her more and more.
No one gets a notification when unfriended, so DIL assumed most normal people wouldn’t even notice.* Unless you deliberately seek out the activity of this person you loathe, then you freak out and break your computer when you can no longer crap on them over the internet. So you save up all that crazy for an hour + long tirade of nonsensical self-serving gibberish including accusations of how you knew Son was a horrible person way way back from childhood, unfriending your son on his birthday (no card or present for him either, that’ll make him sorry for being mean to his wonderful mommy by “letting” his wife unfriend you from facebook, ha! And block both of them so even if they wanted to send you a friend invitation they couldn’t.) and just generally acting like a nutjob. And it will all be DIL’s fault. And you’ll make sure everyone you know or have ever met knows this.
And yes, before the unfriending, you will tag DIL with stupid quizzes and drinks and notes and boring political links, because you have nothing better to do than be on the internet all day long.
At least, that’s how you’ll use the internet if you’re my MIL and a complete and utter waste of space. 
*Which shows DIL still doesn’t get it, even after 9 years of the crazy.
How I use fb is just to see what/how my old friends from high school/college/old work places/places we’ve lived/met while traveling are doing, since we’ve moved and don’t live near any of them any more. It’s been really neat to see who contacts you, and it’s been interesting to see how much some people have changed (and how little others have) and see their kids/dogs/fishing photos/random weird stuff. Stuff that’s boring if you don’t care, but that you kind of miss if you haven’t been able to see them in a while.
We used the fb app on the iphone and the ipod Touch to update our family and friends while we were on vacation and share photos–my grandmother isn’t on facebook but my aunt would show her our pictures and stuff, so in addition to all the postcards we sent, she didn’t feel left out at all since we couldn’t call like we usually do. We didn’t have a lot of internet time, obviously, and fb was a good central place to keep in touch.
Obviously, it might have been better to have been more out of reach of certain people, but since the last long vacation we took that we traveled out of the country my mother died and we didn’t find out right away and it made certain aspects of that whole horrible situation worse, I liked being able to stay in contact so easily despite the time zone difference.
So, fb has been a really neat tool and an unfortunate catalyst for teh familee dramaz, but if it hadn’t been that it probably would have been something else, since I think she just felt like she wasn’t getting enough attention and we were probably enjoying ourselves too much and deserved to be humbled.:rolleyes:
(Mods please remove this if it seems like threadshitting, perhaps I should have put it in the mini-rants Pit thread. I actually feel a lot better after venting, which is weird. I’ll probably feel guilty later, after the edit window has closed.)