I also do this. I tell them to do honest and constructive feedback because
their teammates might not know that they are doing something bad (what?
texting all period annoys my team?). It is very easy - I put the file on
blackboard for them to download.

Regarding nasty comments, I haven't had this issue. I do tell them that if I
find their comments inappropriate they will be asked to redo them and they
will be considered late. I have a pretty stiff late penalty (2 points off
final grade) and have NEVER had an issue with bad comments. 

Erica