I love this concrete example of practical coding to do something quantitatively and empirically valuable. Yes, there are great analytics packages, but sometimes you need to do some custom analysis
Thanks! This gem looks interesting but doesn't apply here since with Jekyll you're basically serving static html pages (hence the need to make the A/B split with JavaScript).
I think it's cool you're attacking this.
I think you should check out Google Web Optimizer (iirc), which will do some of the heavy lifting for you.
For example, there's no stickiness here, which I think is a typical best practice.