Design and loading "speed" - well, should be optimized! Regarding the idea itself: Where do you see a difference between SendFlare and i.e. paywithatweet.com or any other sort of those tools? I gave some of them a try during the last years and none of them had this "Wow!" effect - was more like a nice to have, but nothing I wanted to use every single day.
Still: I believe that our social "statistics" will become part of payments 3.0 but none of the tools I know consider my exact data i.e. # of followers on Twitter or friends on Facebook just to name the most obvious ones.