I dislike MSN messenger (ruined many conversations by being rash there; communicating should be eye to eye or at least voice to voice, and if that's not possible - by written messages where you can think over a good reply before sending back) and I've decided against Twitter.
Whenever I want to talk to friends, I use my free sms ^^ And facebook is great for keeping in touch with people you can't meet often, as well as a great way for my new class to keep track of each other and arrange meetings and parties easily. I'm doomed without facebook <3
These are all MY opinions, of course. Goes without saying that Twitter and MSN can be great for all you other (crazy) people.
xD