Twitter

This one's easy. I'm already doing it. I began twittering (tweeting?) earlier this year when some of my favorite entertainers began twittering messages. I actually learned about twitter from their myspace pages. It's been an interesting way to keep up with concert information and the like.

Pros: Pithy comments, to the point, but not abbreviated grammarless messes.
Good for communicating very basic, urgent information.
Easy to protect yourself from weirdos. And I've already met some of those.
By looking at people your people are following, you can meet other interesting people. However, it's also got its limitations.
Recent news events have established the potential of twitter to shape the world; we now have an army of amateur reporters who are capable of making the atrocities in Iran obvious before official news organizations have the opportunity to bowlderize reality into something acceptable and palatable.

Cons: I don't see using this for people I know in real life. I don't think it's a very articulate or effective form of communication for any message of any real depth. If I need to tell my husband that he needs to pick up some bread or my daughter that she needs to remember her swimsuit, I think a phone call, or even a voicemail, is more likely to be effective.
I have seen twitters where people tell their legion of followers these earthshattering bits of information: Going out to eat. Went to see a Mets game. Baked some cookies. Is it really necessary for us to share the minutae of our lives with the world? I don't know that my day to day stuff is all that interesting and I can't think of a good reason why anybody would follow me for that kind of information. However, I've been a very conservative tweeter - I think I've sent six whole messages in my entire life. Twitter sounds like a good way to attract a stalker, if you are not careful. I think I'll stick to finding out concert information, for now. Also - The Onion on Twitter is good for a laugh.