Playon doesn't rewind at all. Maybe it did, I've only had it a few months. Also, as I have been finding out, Playon is basically in Beta, and we are it's Beta testers. They almost always have a new version every week that introduces more fixes and problems.
They have good response times, but you always have to send them your computer info through their system, and then, they just come out with a new version.
I've heard the Roku boxes are trouble free. They're like $99 though.
Anyone reading this, as of November 2009, Playon is just a headache that works only half the time. Skip it, until it works better. I'm tired of "unable to connect" and "corrupt data" every other time.