Up until now, I thought that E-Miles was by invitation only for a specific. I rec'd an email last night inviting me to join for United, but after digging a little deeper, I found a link that lets you choose what program you want to sign up for. Basically it’s a marketing program that will send you emails asking you to review offers and take a survey afterwards. For your efforts you will earn between 5 and 25 miles per survey (other offers award more miles if you sign up or purchase something, depending on the offer). Here's the link Participating Airline programs include: Continental, Delta, United, US Airways, Alaska Airlines and Frontier. Other options include earning points for Hilton HHonors and IHG Priority Club as well as Amazon Gift Cards. I posted this on my blog earlier and a reader had a great idea to use this program for US AIr, and keep the miles with e-miles until the grand slam promo, then transfer the miles to US Air and it would count towards the contest.