Whether I frequently shop with the included stores or not, the opportunity for free shipping from any of them for a year, for free, is appealing. I'm not certain that I'll pay $79 to renew, as I already have Amazon prime, but I'll definitely try it for a year. Even one free delivery with Dominos (instead of paying $2) will make it worth the 20 seconds it took me to fill out the form.
I'm mostly excited to see what future options become available. Toolking looks like it could be a good one, but I'm curious who else will jump on. If someone like Walmart, Target, or Sears, (or hell, home depot or lowes) came on, it would be amazing. At the moment, the included stores have a lot of overlap with amazon prime offerings, but there are a few that have some new stuff, ie autozone and radioshack (as well as the clothes stores). I will say I seriously doubt Sears will jump on, as they currently have their own $79/year 2 day shipping program for it and k-mart.