I know there are a bunch of gunners in the pre-med crowd, less here than on SDN, but I don't like to think of myself as one so I'll tip you guys on to something that could be HUGE for your applications.
I used this service called Essay Edge (
www.essayedge.com) for part of my app. It's a bit pricey ($140 US for 900-1200 words) but they get "Harvard educated" reviewers to critique your essay paragraph by paragraph, and rework the parts that need it.
I consider myself to be a good writer (when I'm not on internet forums) but the improvement was phenomenal. The comments were very specific and helpful, and the reworked essay was outstanding. A good bit of redundancy was eliminated, things were rearranged, things that weren't important cut out and things that were, emphasized. The editor even corrected me on some medical terminology & conditions which came into play in a discussion of an operation my grandmother had. If any of you are thinking about a service to review personal statements/essays, I
strongly recommend essayedge. Ask for Franklyn Ayescu as the editor.