I don't believe it's possible to run Plex Media Center on it yet, though there are forum discussions on porting it to the Pi. But I do know that it can run XBMC

I don't believe it's possible to run Plex Media Center on it yet, though there are forum discussions on porting it to the Pi. But I do know that it can run XBMC quite well and that is why I ordered mine a couple of days ago. I'm gonna turn it into a sweet little XBMC machine which will be hidden behind the tv. Just Google "Raspberry Pi XBMC", there are a lot of reviews and tutorials showing how it's done.