Put simply, Plex version 1.1 is everything that FrontRow should be. For a start, it streams to your iDevice, presents plenty of online media ... you get the idea. The only advantage FrontRow has is price, and at US$4.99 Plex probably won't break the bank.
The latest version includes many new and updated features, like improved subtitle and audio stream selection support, Direct Streaming and Direct Play support.
One interesting addition is TV out and AirPlay support, though the latter is still "experimental," which suggests less-than-optimal performance.
Plex 1.1 also offers much improved live encoding. For example, Plex 1.1 will note what your Apple TV 2 can manage and only convert what needs to be converted, leaving other streams intact.