Twitter and Librarians in the Classroom

An article in last month’s U.S. News and World Report (“Twitter Goes to College“) talked about how some college faculty and students were using Twitter in their classes send tweets during lectures — students could ask questions, post “huh?”, etc., — as a way of getting instant feedback on the class in process. Such “backchannel” behavior is common at library and technology conferences, but appears to be rising in academic settings.
This could provide another ‘in’ to the academic process for librarians — being able to monitor a lecture in process and jump in with tweets of resources that might help the students understand the context of what is being discussed. A single librarian monitoring several classes at once could provide ‘on the spot’ reference services without needing to be in the classroom or interrupting the flow of the lecture.
Are any librarians or libraries providing, or considering offering, such a service to faculty and students?