Taking a break from social networking sites and random time-killing online activities. You still use e-mail and take care of important things (like bills, if you do those online), but avoid instant messaging, YouTube, Twitter, MySpace and Facebook (exceptions: it's the only or best way to get in touch with someone about real-life activities.
The goal is to de-ADD your life and reduce any unhealthy drain on your time and energy so you are more connected to and productive in the real world, ideally making some people happier and healthier who seem addicted to the internet. It can make you more focused and productive.
Being accused of procrastination, stalking/"stalking", having no life, etc. are all signs you need to cyberfast. In some cases, drama magically occurs less and less!
Guy 1: Dude, I haven't seen you on Facebook or AIM in a week! I thought you were dead.
Guy 2: Naw, man, I was just cyberfasting. I get too addicted to cyberspace sometimes! I never get anything done.
Guy 1: Oh, snap--I should do that. Some girl thinks I'm stalking her just because I LOL at all the funny crap she posts all day.
Guy 2: SHE should cyberfast, too.
Lindsay Lohan went on a cyberfast and everyone thought she had been kidnapped or gone to rehab when she disappeared from cyberspace for a few weeks.