Take a look at the case study below where 37Signals tested different kinds of headlines (and the winning one boosted conversion rate by 30%).
Highrise Headline test – 30% increase in conversions
The winning variation said “30-day Free Trial on All Accounts” and worst performing variation said “Start a HighRise Account”. Note that clear, no-nonsense headline won. If you think about it, if a visitor is on Signup page he obviously knows that he is signing up for HighRise account. The winning headline clearly convinces the already interested visitor that there is nothing to loose as they offer a 30-day free trial.
Another example of how much headlines matter: CityCliq, a startup in local marketing industry, split tested the positioning of their product.
CityCliq headline test: 90% increase in conversions
Here are different headlines they tested: