Well Roku users can rejoice today, as Plex has released a tv app for all Roku devices. Plex, a fork of the XBMC code, is continuing to integrate with more hardware with this release. Just last year, Plex was an OSX only app. Now Plex has clients for Windows (even a media server for PC), LG televisions, the latest Apple TV, Android and iOS (iPhone/iPod and iPad). Linux support is said to be coming soon.
Plex has a great setup for users with multiple screens. Plex uses a client/server architecture which involves one central media server which chronicles local media (and various plugins to third-party applications and web services). Clients then connect to this central server to consume content and rely information back to the server (how much was watched, for instance). Therefore, one can pick up on a TV show from where he left off on any screen.
Most of the clients use a transcoding-on-the-fly engine from the server to consume content. So, regardless of source video codec, any device can stream. The Roku app uses this technology, and is reported to handle up to 1080p video content.
Photos of the app below are from the Plex Blog Post: