Twitter

Twitter is a service for friends and family to keep in touch with each other. It also keeps thing simple that other chat services don't. If you are using twitter on the phone then it will just instantly let you know that you got a status update instead of looking at everything else that you don't want to look at. You also can get cute twitter backgrounds to make it more interesting. It won't just be a boring page with nothing to look at.
I think twitter can be good for a teacher because if you have a hearing impaired student in your classroom and they weren't financially able to afford the technology then the teacher could tell the student what the assignment is regardless of they are in the classroom or at home. Also it could be good for a teacher because other teachers can communicate with it by sharing their ideas of things on twitter or informing teachers about other things that are going on.
The negative effects of twitter could be that students and teachers could be easily distracted by all the technology and not want to stay off of twitter because you are socializing with people you know. Another negative thing about it is that everyone doesn't have access to a computer or a phone with internet on it.
As a teacher I don't think I am going to use twitter in my classroom unless it is necessary and as an individual I may use it eventually.