This is mine. 2 weeks ago I set out to learn how to write android apps, and do gaze tracking. Story here: http://blog.chewxy.com/2014/04/08/eyetracking-jetpack-joyrid...
The result is http://eyemap.io. It's a simple-to-use, affordable gaze tracking analytics system with your tablet. I'm still testing if people actually want the service. It's hard to make sense of it, because people sign up to the mailing list but nobody would pay for it.
Curious how you approached that!
What I did to measure accuracy was to draw targets on the screen, and focus my eyes on them. The error the absolute distance from the estimated pixel to the actual target pixel.
To answer your question - on a Nexus 10, there is a expected error of about 0 to 160 pixels radius in office lighting conditions.
As for small movements, I use the full resolution video of 1344xwhatever, which gives a lot more leeway in terms of movements. The movements are then smoothed over time using a moving average over 8 frames, and another smoothing algo uses a pyramid kernel.
TL;DR: lots of algorithm. Quite a number are dodgy.
I would also try partnering with specialized cloud hosting solutions like * https://www.heroku.com/ * http://www.acquia.com/ * https://www.getpantheon.com/
Unless you are seeing keen interest from people willing to pay for this directly in its current form, where I would research and learn how website or app optimization platforms market themselves.