deadsea - 10:36 am on Aug 11, 2011 (gmt 0)
We do tons of A/B experiments on our site (millions of pages). From an SEO perspective, we try to make sure that the titles, meta description, and links on the page for SEO don't get touched by the experiments. Other than that, the experiments are generally run by non-SEO knowledgeable marketing folks. They often do some pretty dramatic changes and we haven't seen any SEO problems because of it.