A psychometric consulting firm named AptiQuant asked 100,000 people to take an online IQ test, and then correlated scores with the web browsers used to take them. The blue bars represent test results from 2006 and the red bars test results from 2011. The vertical axis represents IQ points. Link -via Geekologie
UPDATE: The story was a hoax. Thanks to commenter che.
I regularly use two. Sometimes it depends on the site I'm visiting.
apparently the study is bogus.