I recently gave a talk titled "7 App Store Tips" at the Dublin Web Summit.
One of the tips I discussed was the use of an in-app alert, which reminds users to rate/review your app on the App Store.
I've since tidied up my code a little and uploaded the class for re-use within your own apps.
Usage:
VCReviewPopup* popup = [VCReviewPopup sharedPopup];
popup.appStoreURL = [NSURL URLWithString:@"https://itunes.apple.com/ie/app/eirtext/id286099297?mt=8"];
popup.numberOfDaysBeforeShowingPopup = 14; // Show alert after two weeks
[popup showAlertReminderAfterDaysHaveElapsed];