I watched this video (it's not in English, but you can see what's being done) and thought it looked easy enough that my mom and I could tackle it in a few days (well, she was able to!).
it's a basic macrame knot around the straps, with beads strung on one of the ribbons. I used the thinnest ribbon they had at the craft store, 6/0 seed beads, some polymer clay beads I made forever and a day ago, and the middle beads at the toe were just flat glass beads.
if I'm lucky, I'll be able to do another pair this summer, but I really wish I had the time to make a pair like Luis Quintero - I love watching him macrame sandals, even if I have no idea what he's saying!