I've been wanting something like this for a few weeks.

As Kuroi stated, if the emails are worded effectively, such a module could become integral to anyone's site. Personally, I place a lot of value on reviews, both as a customer and a site owner. Customers like to know that previous people have made the purchase they are about to make and more importantly, have been satisfied, and this would surely increase how many a site receives.

Sure, some people will disregard the email but I don't believe it would make them think the site owner is being pushy. We all know Amazon do the same.

My current workaround is to leave a short message on my checkout success page about reviewing once their order is complete, I feel that people would just forget this straight after.