The has been a lot of discussion lately on the issues related to privacy on Facebook and other web 2.0 applications. The straw man argument would be, "Well, you don't have use them. Nobody is making you." The fact of the matter is that we do in this day and age and depriving students of the necessary skills and guidance with these tools puts them at a disadvantage. Would it ruin their lives if they didn't get the experience and instruction? No. But it does put them at a disadvantage in our current global environment.
Part of the problem has been created by ourselves. If we had been teaching students how to use computers and technology beyond word processing and creating PowerPoint presentations for the last twenty years, our students wouldn't need Facebook to collaborate and communicate. They could be creating their own social networks, just-in-time, when they are needed and have complete control over their design and data. Imagine if you could roll our own "Facebook" as simple as creating a PowerPoint presentation. The server, database, and your code, all in your pocket, or stashed in your sock drawer at home available to those that you choose.