At the start of class today, one of my students excitedly proclaimed to the class that I'm on Wikipedia. And then was promptly scolded by others of the class for invading my privacy. Which was awfully sweet all around, but it's okay, folks. I'm pretty sure that privacy ship has long since sailed. :-)
I do tell the students on the first day of classes that they're free to friend me on Facebook, follow me on Twitter, read my blog, etc. At their own risk. I usually say something like, "You may learn more about your professor than you actually want to know"