essentially, some tips on how to let google know you aren't trying to game the rankings - show the same test to all user-agents, use 302 redirects, and keep it short for goodness sakes!
common sense note - if you don't have a significant number of samples, you're just pretending to be scientific..
Google posted some guidelines on how you can conduct A/B or multivariate testing and stay clear of any issues with being listed in its search engine, such as avoiding penalties.
via searchengineland.com (click through to read the full article)
image: ladyleet blog