You probably know that Gap, Banana Republic, Old Navy and Piperlime are owned by the same corporation. You can use your card from one store at all of the other stores, and they all do a ton of cross promotion with Piperlime, the shoe site.
A trip to one site is frequently followed by a trip to one of the sister store sites - can't find that white shirt at Gap, go check the other sites.

The Company just made it easier for us to do this by putting fast navigating tabs to the other three stores on all of the sites. Plus, now you can put items from all four stores into one shopping cart, and check out just once.

It's marketing genius, and we like how easy it is to switch between the sites. Plus they're doing a $7 flat rate for shipping, which is nice. For more details, check out their information page.