Let's talk about the nerdy interesting bit. It seems that MileagePlus has rolled out some sort of Facebook Connect type system for registration / mileage transfer at WallAndMain.com (and presumably will work on other sites in the future with your MP credentials):



Pop up is a URL at https://secure.unitedmileageplus.com/CM_connect.jsp with the usual amount of URL params to define who the partner is, security key, blah blah blah.