One thing you're going to want to consider is the fact that people currently on your law review or alumni of your law review will get offers or have jobs at many of the top firms in the area around your school. If you slack on law review and then put it on your resume, I can see an employer contacting you EIC or asking an alumnus/a from that review about you. If you're lazy it's going to be real tough to get by that. Also like Jacy said I'm sure explaining to an employer why you got kicked off LR is no fun. I don't know how your review does it by our out going board 3L's will chose the new board from the staff. If you're lazy you're getting the dubious "senior staff member" title your 3L year instead of a real board position. Why would you write a bad note anyway. I am hoping to get my note published and if it's bad I know that can't happen.
This can be highly school specific, but isn't there a lot more rising 3L on LR than there are editorial position? In that case someone must become senior staff member. There is nothing wrong with that.