I admit that I'm still not an avid user of twitter like some people are. I rarely post things and usually it's a retweet. I've stopped posting anything personal, mostly because I don't think what I'm doing right now matters much unless I'm sharing something educational. I.E. I don't tweet stuff like "Off to Lunch!"
I do however learn a TON from twitter and I hope that in the future, when I'm actually working in the library I'll use it more, share more etc. My favorite people to follow are the ones who share fun an interesting ways they are using tech in schools or libraries. But I admit I also follow a few other types. There are some fun YA authors that I follow. I also have some scrapbooking people who share tips and tools.
I have not figured out the best way to use these tools with the kids yet. In fact, I'm not sure how much students use Twitter. I think there are tons of ways to get information out to people and that is one that may work for some and not others. As for other Social Networks, such as Nings (these are great for specific communities and we use them in our school) and Facebook (which can reach a ton of people) there is potential for both professional growth and connecting to our students and their families.