That's what I'm doing and it works very well. As a media device, it's the best option I've found. Built-in wireless, fast CPU, lots of RAM, supports Netflix, Amazon Instant, Hulu, XBMC, Pandora, and more. Roku has more channels available, but doesn't have any options for streaming content over a LAN.
I played a few minutes of Minion Rush on the Amazon Fire TV. It had some laggy moments, certainly not the gaming experience that they claimed it would be.
Plex is terrible. It requires transcoding audio and video on the fly, which requires a hefty media server. XBMC decodes everything on the fly on the local box requiring no transcoding.