I don't know about MOST helmets, but mine came with a longish strap that whipped around and beat a tattoo on my head whenever I got up to 60 mph or so.
I complained about it to my Dad, and he showed me a neat way to thread the helmet strap through the D-rings so that it takes up the slack AND acts as a "quick release" mechanism. He said he learned the trick long ago from some OTHER old-timer.
Click on a picture to see a larger version.
I've been securing my helmet this way for 20,000 miles now (June 2003) and my hands do it very quickly without my even thinking about it.
Some people that I have shared this tip with have expressed concerns with its safety. While I understand where they're coming from, experience has shown me that it is every bit as safe and secure as the "normal" method. So don't knock it until you try it - at least once!