After adding your Movie/TV-Series folder Plex starts to automatically indexing your media, downloading meta data and providing it in a nice interface.
You get stuff like DVD covers for you'r favorite shows or movies and if you select a TV-Show the intro jingle starts to play and you see reviews of each episode you own.
Plex integrates content from iTunes and iPhoto as well as allows the user to manage all video, photos, music, and podcasts from a computer, optical disk, local network, and the Internet using an Apple or Harmony remote control. It also features an own 'app store' digital distribution platform called "Plex Online" with a growing list of community driven plugins for online content like Hulu, Netflix, and CNN video.
The interface can be skinned and is very customizable which adds to the user experience and you can also stream the media to another mac,iphone or even android.
It supports nearly every known video codec and subtitles and you wont use any other mediacenter again :) and the best part: its completely free!