Here's a couple of updated pics of my setup for people with media machines that are on the fence.
Here's the full Plex install w/media server on the mini in my living room. Everything streams wirelessly from a NAS hanging off of my router upstairs.
Media view / different section. (You can define them yourself and use separate media scrapers for them. Eg: I split off my music videos from regular movies, TV shows, etc.):
Now here's the TV upstairs in my music room, where the Roku is. Again everything is wireless. The Roku plugin is fed by the media server, so any changes there (added content, etc) are immediately updated on the Roku.
And a couple screenshots (remotely controlling the mini). Here's the media manager:
And list view, with paths and such:
Plex Media Center is an unstable turd sandwich on Win7, btw. Looks like that last system at my house running Windows is going Ubuntu as well.