Here's a great post about the negative aspects of teacher recasting. I find that I automatically "echo," or recast what my students say. Half to say it correctly and half so that the other students hear the thought. The articles points out that not all communication needs (nor should) go through the teacher. This is neither authentic nor useful. I have always wondered why some students complain that they can't understand their classmates, and this may be one of the reasons. The students rely on me to negotiate for them, rather than negotiate for meaning themselves.
Do you recast what students say? Why or why not? If you're a student, would you prefer if you teacher didn't always repeat what you and your classmates say?