Ask HN: What would you like to know about A/B testing?

I'm a developer at a CRO agency and I'm thinking about writing a small ebook about A/B testing and Conversion Rate Optimization. I've worked with over 30 clients, mostly in the eCommerce space and I'd like to get more ideas from the HN crowd which I suspect is skewed more into the start-up/SaaS side of things.

I'm wondering how many of you are A/B testing. And by that I mean, do you have a clearly defined strategy or is it more like "we installed A/B testing software and are just randomly testing things"?

Any answers/questions/thoughts are welcome. I'd like to get a better understanding of the gaps in the public knowledge of A/B testing.