There has been quite a bit of interest in the Third Party Clients forum over the years, but I do not believe any active development is on going.
EDIT: Please dont forget to upvote the top post, as I believe that is how Plex tallies votes.
EDIT 2: This should be QUITE easy now! The new TiVo boxes use the Opera App Store, which is HTML5 based! REALLY hoping Plex can create an app for this - should be quite easy based on the existing Plex/Web!
ALSO: Several SONY Televisions use the Opera App Store, making this proposed App even more useful!
Yeah it's portable and easy as flash.. but really flash apps suck most of the time because most programmers don't know how to do it right. The ones that can do it right usually have to work with limitations of flash that makes the app suck.