US AIrways is offering a 50% mileage bonus on purchases with participating merchants made through the Dividend Miles mall through June 30. Registration required.

Up to 10 shopping transactions are eligible for the bonus, and transactions must post by August 30 with a transaction date not later than June 30 in order to be eligible.

This is stackable with the shopping bonus for Dividend Miles elite members that runs through February of 2011 (25% for Silvers, 50% for Golds, 75% for Platinums, and 100% for Chairmans Preferred).

A Chairmans Preferred member who registers this offer and shops at FTD by June 30 would earn 50 miles per dollar, whereas a non-elite would earn 30 miles per dollar.

Since the earn rates on the underlying shopping purchases themselves aren’t stellar this isn’t an opportunity to load up on miles simply by shopping for items you wouldn’t otherwise want. Still, it’s definitely worth registering in case you wind up making a qualifying purchase.