I just signed up for a starbucks card today, so I can get free wireless access. The iPhone app is better because I wouldn't need to carry my card with me. I know I will lose it or not bring it.

The ability to reload money on it is an advantage as well. Not sure if there is anything advantage to a starbucks card in general; discounts, give aways, other than the wireless, but I like the app approach over the plastic in my wallet.