In the iPhone 4 beta, when you delete an app you are not asked to rate that app as you are in iPhone 3.0. Whether this functionality has been removed from the iPhone OS going forward, however, or is merely removed from the beta so people don't rate apps based on beta behavior is unknown.
Many developers have long had issue with the "rate on delete" function introduced in iPhone 2.2. Making it easiest to rate an app when you were removing it was thought to unfairly favor lower reviews.
We'll have to wait until this summer's official iPhone OS 4 release to see if it stays gone. In the meantime, let us know what you think. Did you use rate on delete? Did it make it easier to rate lower quality apps? Did you go to the App Store to also rate your preferred apps? And do you want to see rate on delete removed or do you hope it's back in the final release?