It turns out, this particular service is new, but it's not an unfamiliar concept. I'm sure you've seen authors signing autographs on readers' Kindles in lieu of traditional pen to paperback. This idea is similar, but it's something you can do from home to interact with readers (or your favorite authors).
You can watch the video here, which explains the process. It's surprisingly simple.
Dawn, the beta reader who blogged about her Everlong/Evermine experience, was my first victim. You can barely see my signature, but the rest is bold and clear. It's got a lot of potential. I'll be keeping my eye on its development for sure.