When you use the app you can register or unregister your cards, reload your cards, check balances, edit profile information, check your rewards program information and more. I'm also told that sometime this summer we will be able to reload a Facebook friend's Starbucks card as a gift through this app. Please don't tell my kids about this upgrade.
I think Starbucks has found a great way to leverage over seven million people who currently "Like" Starbucks on Facebook.