I often hear that you should delete your search history, cookies and if possible change your IP when looking for flights online. The reason is that otherwise airline websites know that you're really interested and will increase prices. From personal experience, I had once the same impression when I first looked for a flights a couple of days in a row and got only high prices. Then I did the same at work with a different computer and got way lower prices. However, this could be a coincidence.
So my question is: Is this just an urban legend or is there really evidence?