A collegue of mine was speaking to her students about filters and limited student access to the web during class. Some of her students made the arguement that it was less distracting for them to have web access. Without web access during class, the option is games, but games demand too much attention. With the web open, games are abandoned for social networking which the students argued was less distracting. One sends a message and then can return one's attention to class.
I don't make this stuff up. Really. I don't have to.