I've talked with several teachers who are very excited for Google Classroom to come out. I just came across this blog post on Twitter from a teacher who did a Google Hangout with one of the case study schools and it will answer some questions folks may have in regards to using it in their own classrooms this fall. I'll admit that it made me even more excited to get my hands on it! Click here for the link.
I had a teacher ask me if there was a way to hide or remove students who are no longer in your class. The answer is maybe. It depends on if they are officially dropped from your class and appearing as red in your roster and gradebook. If not, then no, you cannot remove them until they have been unenrolled from the class. If the student is showing up as red in your gradebook though, you can hide them so you don't have to worry about them. Here is a screenshot to help you do it: