Yes!
We went on June 19th. Even though it was a Sunday (and Father's Day, at that), the park wasn't very busy. They were putting them on everyone's wrists as soon as you went through the turnstiles.
When you went to go on a ride, you tapped your wristband to the kiosk. It would give you a return time. For most of the rides, the return time was only about a few minutes after the current time. At most, it might have been 10 minutes later?
Things seemed to run smoothly. I wanted to go back and test it again when the park was really busy, but we didn't get a chance to.
DBF and I were talking, and we seem to think it will work better at VB, where there will be a hub-and-spoke pattern in the park. That way you have things to keep you busy while waiting for your return time, and you're not all the way at a dead end, making it a little inconvenient to trek back to the middle of the park.