A lot of Slashdotters seem to ascribe no value to Twitter, or maybe they're just more vocal. Here's my experience, and a general comment on the social media scorn we read here.
Like perhaps many geeks/nerds I'm not a very social person, but I used a Twitter client that let me see messages from people in my local area (Sydney), much like an IRC channel except people write from places other than home/work. After a while of reading and occasional replying I found it quite enjoyable, followed a bunch and and managed to become somewhat friends with some.
There's no fundamental difference between IRC, a forum, Facebook or Twitter; they are all mediums of socialising. Slashdotters laugh at the last two because they are seen as "not special", which is true, but not the same as being "of no value". My local Thai restaurant is nothing special but that doesn't mean it has no value.
On Facebook, I understand the scorn that you don't want to be friends with classmates you never cared about then or now. But you don't have to use it for that, so it's like complaining that you don't like pad thai (I don't) so why go to a Thai restaurant? One of the reasons Facebook provides groups, fan pages and even apps is to provide other ways for you to interact with users. Yes some of those apps (like the quiz ones) are VERY annoying, but a small number of apps have been pretty fun and addictive (generally trading games) and I've made a few more online Facebook friends that way, people who I otherwise would never have met or interacted with.
It has been ephemeral, some of those people I don't talk to much anymore. But that is just like IRC and real life, where some of my friendships have lapsed over the years and new ones have taken their place. People move in and out of our lives, and Facebook and Twitter are just another ordinary way for this to happen. They are not worthy of the hype, but neither are they worthy of the derision.