so lately I've been wondering, if there's any research on efficiency of content teasers, and by that I mean blurred content (for example: answers to questions) with registration button. My main concern here is credibility - will the users belive there's actual content underneath the blur, will they see enough value in this, that they will register?
I'm going to go ahead and suggest diminishing returns may be a reason not to force people to register.
Unless there is an underlying monetary business model that you cannot get away from, and even if that is the case there are reasons for loss leading, say an answer forum, giving away the first answer and blurring subsequent searches.
Back to the original question, I think a nicer user experience, notwithstanding what was said in the above paragraph, is to show users the content and gently coerce them into giving you their details.
You've already achieved part of your aim in driving the traffic to your site. A word of caution, sites that plonk registration forms in modal boxes on top of a web page can have a detrimental effect on registrations. Subtly providing the means to register on the same page and keeping the initial details to a minimum could work wonders.
Answered without knowing what you are teasing your users with!