I've never done the Groupon thing before but browse occasionally and have heard of some great offers through the board. I hesitate to buy one in advance because it never fails, our plans change on the spot and I could see wasting one. If I download the Groupon app, can I buy one and use it the same day? Say I'm at Paris and I want to get the $30 for $15 at the burger place - can I buy it on my phone and then immediately go in and use it? What do they do - send you a code via email?