Adult sites have been using disclaimers and enter-buttons to "prevent" people under 18 from entering their site. Underground hacking sites are also adopting this practise. There is something different about these disclaimers, though. They commonly seem to prevent everyone from entering the site. Putting a site on the web and denying access to the content from everyone seems a bit illogical at first. Or what do you think of the following statement found on one site's disclaimer: "You must be at least 250 years old and own a pink car to enter this site."
Pink car... checked. By the way, as you can see from the photo (taken by Micke), we barely have any snow left here in Helsinki but the sea is still partly frozen.