Yeah the Roku 3 is much snappier when it comes to loading channels and switching between feeds. The interface is also much nicer but that's due on the Roku 2 any day now. Search feature is incredible and I see that being ripped off a lot in the future.
Also much better performance with Twonky.
Is Twonky different from Plex?
I don't have any experience with any of this, it's all Greek to me.