Appbot is a simple, free service that emails you a brief overview of App Store comments your app has received in the past day or week. You sign up, add your apps and the very next day the roundup is in your inbox.
I use a few other services and apps to track comments, but find the quick morning summary that Appbot offers quite handy, particularly if you’ve just released an update and want an “executive summary” of the mood on the App Store, without having to dive into another app.