I really like the small form factors, it makes everything more challenging and exciting. However in my country, I can barely get a good ATX case for a decent price, and let's not talk about watercooling. So I am still far away from all of this.
Why not just get a Raspberry Pi for 35 bucks or whatever and load XBMC to that, add a powered USB hub, hook up external HDDs for video storage + load Netflix/Hulu onto XBMC. Way cheaper, just a thought, I plan to do this when I am not busy building a LiteCoin mining machine.