A/B testing with Jekyll (and Google Analytics)
biasedbit.com
biasedbit.com
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.
Have you played around with some of the Rack based gems out there like Split?