I'm happy to announce AppMonitor, an app for notifying you about new ratings, comments and purchases of your apps.
I developed AppMonitor because I myself was going crazy constantly checking for changes to these stats: I'm passionate about my apps and always curious about how they are performing on the Android Market. For me it is also important to respond rapidly to user comments, and AppMonitor lets me do just that.
AppMonitor requires Android 2.0+. If you want to be notified about new purchases, you must provide AppMonitor with a Google Checkout Merchant ID and Key; notifications about ratings and comments do NOT require Google account username and password, but they do require that you grant AppMonitor access to the Android Market.
If you want to check out AppMonitor, the QR code below links to its Android Market entry. If you are browsing from your phone, you can also use this url. AppMonitor sells at £4.99 (roughly $8).