There's no need to run Plex on a dedicated server any more.
WD announced its My Cloud NASes now support the popular media server.
Theucs is now bundling Plex with some of its high-end NASes.
Updated - We take a second look at a NAS-as-HTPC, this time using ASUSTOR's AS-604T. It's a work in progress.
You could win a kit of Insteon Home Automation products!