I just want to add that after using a desktop pc, laptop, PS3, Wii, Xbox 1 and Xbox 360 and an Android box media player,none of them have run as smooth and as reliably or as quickly as my Roku 3 with Plex for local content.
WMC or the extender,XBMC and even Plex home theatre on a dedicated PC are good, but they seem to lack either ease of use or specific features that the Roku simply does natively.
The final nail in the coffin for the alternatives is the awesome headphone jack in the controller for my listening pleasure while the wife is asleep or if i want Pandora tunes in my ear while working in the house(albeit not far away).
Now if only i can get Popcornflix and Frightpix to work without a VPN, like Crackle and and i will be stellar happy.