Really, really good - in fact, I have seen people do the same with the 20$ android media sticks that you can buy off dealextreme or someplace.
A great alternative to chromecast.
Free server software, in a dead simple installation package, with config and streaming through a pleasant html5 UI. Smart TV app also free. Small but not insignificant charge for iOS and Android clients. Small SaaS charge to provide dynamicdns /remote streaming.
It's so much of what Boxee aimed for and failed. I like hacking on things, but Plex works perfect out-of-the-box. Really impressed ever since I started using the software a year ago.
But I agree - plex was worth the purchase of the mobile app.
Plus Im running 12.04 - which is a old, stable release - so should be more in sync with upstream debian.