Social networks, like other forms of social media, holds alot of potential to do good and harm a PR practitioner. I think the best advice I would give to a fellow PR rep (and myself) is to choose wisely about what you disclose when thinking about your clientel. external vendors and other relationships you create in your career.
Some people like being able to communicate fast and easy through sites that they are already subscribed to (i.e. Myspace, Twitter, Facebook etc). But what if you are subscribed to a site that half of your clinets are not? Pay attention to generational differences, and even personality differences in the clientel and internal/external partners at your job. I still appreciate a phone call from my doctor's office reminding me of a visit and frankly think it would be too weird if my Doctor's office asked me to be a friend on facebook. Personally, I use Social Networking site to talk to close friends, and have never used Myspace/Facebook to communicate with a potential employer or customer. At least, not at this point. I'm easily swayed by whoever is on the 'bandwagon' in many situations, so if the pressure builds, i'll probably cave.
I think the biggest thing a PR professional could do when creating a page of their own on a Social Networking site is to keep the information about you to an absolute minimum! For instance, if you love Barack Obama and your client is an avid McCain supporter, that could easily alienate the relationship you are trying to build. Put information about your job skills, past projects, professional associations and professional awards you've received. It is very important for clients to see and read the same things as you would tell them in real life. Let the personal disclosure information come naturally through conversation, if you and your employer feels it's appropriate.
Do research. One of the basic lessons that 100-level students understand learning about Public Speaking here at Missouri State is to analyze your audience. You will have to conform to them. Remember, you are a leader, an organizer and a service provider, so act that way.