I've successfully installed ubuntu on a cheap Android TV stick ($40) and then install Calibre on it. It is now running full Calibre content server and Transmission (bittorrent client) 24x7.
My setup is storing all my ebooks library in my Buffalo NAS (2TB Linkstation Live) and let Calibre full program running on my the Android TV stick, and access (read/write) my NAS via the built-in wifi. I also use eNews recipes to retrieve enews automatically;and run many bittorrents on the same stick.
I'm now able to download any of my ebooks when I am away from home; and also control my bittorrent session too.
Details of my setup is here (sorry, it was written in Thai, you may need Google translation to give you some idea how I did it).
I'm willing to answer your questions; but please bear in mind, I have very little knowledge on ubuntu. I learn a bit ubuntu from this project.
This setup consumes only 4.5 watts (wifi on all the time).