Apple has changed the review process to be less biased. Not sure when it was (somewhere around 4.0 launch last year) but they no longer prompt users to rate an app during the uninstall process.

I too really dislike being asked to rate an app. Especially since there's never a good time for this. Most of the time I've see this on my phone is when I launch an app for the 5th or 6th time. I launched the app to use it, not to review it.

We all hate the bad reviews. But don't start doing this. It's just bad user experience.