What are people in ELT twittering about? Is it useful to me and/or my learners…?
According to TIME magazine, "Twitter is on its way to becoming the next killer app…" (as Twitter is proud to proclaim on its home page).
From long experience, I would suggest that a healthy dose of scepticism is always called for whenever the words "next killer app" are used, be it Twitter or Second Life or interactive whiteboards, or any new bit of technology.
"Are my learners actually going to learn more, if I use this?" — that would be the first question I think you should ask yourself as an English teacher. What are they (as opposed to me, the teacher) actually going to use the technology for, to do what, that will ensure that they learn more…?
If you can't see answers to those questions, I'd suggest you hold on before you jump on the latest digital bandwaggon.
I'm not a Twitter user myself, either personally, or for use with my classes: I just can't see the answers to those questions…