Peer editing is absolutley a good way to improve papers.  Not only does it allow my peers to show me some things that aren't right in my paper, but I can tell them too!  Finding problems in other people's paper I feel will definitely improve my writing skills, simply because I will be less likely to make the mistakes my peers made in papers.  What really makes peer editing awesome is diversity.  Unlike regular papers, there is more than one person grading it so everyone's going to put their own diverse input in which makes peer editing unique.