Social networking can be a powerful tool for reconnecting socially and possibly even leading to networking and business opportunities. But, you also have to be aware of the dangers when it comes to your career. Our recruiters routinely do Google and other searches on lateral and new recruits. They don't want to read everything; they do want to look for things that may show a lack of judgment or embarrass the firm. So, if you have a personal webpage listed on your Facebook account, and your personal webpage has pics of you drunk/half naked, etc., these are not going to help your career. I am a fan of social networking, but you need to use it cautiously. I just saw someone comment on another person's wall reminiscing about how they used to do mesc and ecstasy at a local establishment. Why would you post that publicly?
On Facebook, you can use the privacy controls to make your profile private and available just for your Friends. This is a good idea. If we can't access your information, that generally shows good judgment. On a related topic, beware what you post in your own name (versus anonymous) as comments on blogs, message boards, etc. These too will also come up in searches.
Feel free to connect with your friends through social networking. In fact, it is what I recommend in terms of connecting and reconnecting and expanding your base. Just remember who has access to your posts and remember that what you post -- even to your friends -- could easily be forwarded around.
When I was a junior associate, someone once taught me as to an email or a memo: if what you wrote ended up on the front page of the New York Times..would you or your client be terribly embarrassed? If so, don't write it.
Be social, but be safe.
And, on my earlier subject, what have you done this week to further your career?