I have mixed feelings about it. It's easy to use, quicker to get information out, and has the plus of being able to engage all the students at once where they can all interact with each other in once place.
But I also think it can get inappropriate pretty easily. Most teachers/professors use separate, non-personal accounts for classes - Which I think is good (And I'm pretty sure it was required for High School teachers not to give out their personal accounts). But students don't often do that. It's putting out and sharing information that I don't think students and teachers should share with each other. I also think it's much easier to blur the line between friend and teacher with something like that.
If the student is careful and aware, I think it's a good thing, but it definitely shouldn't be the ONLY option for students to get their information from.
My sister made an account specifically for a similar reason. She doesn't use it for anything else, just not interested in it.