Preview at WWDC likely in June, followed by September launch.
Apple Removes Old Non-Customer Reviews from App Store
In September, however, Apple instituted a new rule in which customers could only leave reviews on applications they had actually purchased and downloaded. Existing "reviews" from these non-customers, however, remained in place.
That is, until yesterday. It appears that Apple has removed these early non-customer reviews. Several long standing apps have seen dramatic decreases in their review counts. SEGA's Super Monkey Ball count dropped from 4197 reviews down to 3710 while Namco's Pac Man dropped from 395 to 122. MacRumors forum users have noted that it has been these specific non-customer reviews have been targeted and removed.