Professors and employers alike will advise that you should very carefully manage your online identity. What you post on Facebook or Twitter has the potential of being viewed not only by your peers, but also by a potential employer. Kelli Matthews of PRos in Training sums it up with, "If you don't want people to know about some facet of your life either a) don't do it or b) don't put it online."
I think this is great advice but it leads me to wonder about the aspects of your life that you want to share with certain people and in a certain context. For instance, many people will tell you that you should not have photos of yourself with a beer in hand on your Facebook page. In my "real" or "offline" life, I certainly don't broadcast my partying habits to the world, but friends, co-workers and even my supervisors are certainly aware that I'm social and go out from time to time.
In the same context, I think that it is acceptable to show photos on Facebook that paint the picture of myself as an outgoing person who enjoys social activities with my friends. Katie Horley of The World of PR According to Miss Horley wonders if she should delete her Facebook account altogether for the purpose of maintaining a professional identity and settles for cleaning up photos and utilizing privacy settings. These are great steps. For me, I think I will continue to keep the same approach that has been working in real life - by communicating myself through a mix of activities that show I can be professional and have a lot of fun at the same time.