I could see using screencasts many ways in the classroom. I like that the students can embed their video into Kidblogs so others can see their explanations and offer comments.
I will be implementing this awesome tool in the fall with my first graders. My brain is already spinning the many ways it could be used. Here is a my very brief hand at using Educreations. I think it's best to have a pre-written script so you are not fumbling over words.