My general goal is to have at least one, and preferably several A/B tests running at any given time across one or more of our marketing sites. There’s no “perfect” when it comes to marketing sites, and the only way you learn about what works and doesn’t work is to continuously test.
Quick read on how 37 Signals use split testing to increase signups for their Highrise continuity software product. Most important notice how they are tracking right through the CRM to see the effect of each test on lifetime client value. Small hinges swing big doors!