I got the Amazon Fire TV 2 days ago, plugged it in and got up and running pretty quick.  Amazon actually links your account info when you order direct and all you have to do is connect to network.

Setup couldn't be much simpler.  Plug in power, plug in HDMI, put 2 AAA batteries in remote and power on, enter in wifi info, watch an intro video and you're off!

I was able to watch a few 'free-with-Prime' membership episodes with no problem starting out.  A few episodes into a show I had to make a phone call so I paused my fireTV and was gone for a good 15 minutes or so.  Came back, and the screensaver was on.

I could not get out of the screensaver.  No button presses on the remote worked.  I took the batteries out (supplied btw), put them back in and the remote worked.