The Mac OS X Lion Up-To-Date upgrade is available at no additional charge via the Mac App Store to all customers who purchased a qualifying new Mac system from Apple or an Apple Authorized Reseller on or after June 6, 2011. Users must request their Up-To-Date upgrade within 30 days of purchase of their Mac computer. Customers who purchase a qualifying Mac between June 6, 2011 and the date when Lion is available in the Mac App Store will have 30 days from Lions official release date to make a request.
http://www.apple.com/pr/library/2011/06/06lion.html
Apple's up-to-date page doesn't have much info yet though. This time, it will be completely free as there are no costs related to the media and shipping.
Didn't see this anywhere else yet so thought I should post this.