Both Plaxo and Linkedin are useful sites. I found many work related people I knew on Linkedin. I think as I grow professionally, using these types of websites will be helpful. I can keep all of my professional contacts and personal contacts information in one section. These sites are more for social networking with colleagues and other professionals in your field.
MySpace and Facebook are more of social media sites to share whats happening in your everyday personal life with your friends. Facebook and MySpace should not be used as a social meeting place for those you work with. I feel that it is unprofessional to share private aspects of your life to the entire world. Things can be posted that could potentially put your job and reputation at risk. It is definitely not a risk I am willing to take. As an example, we were hiring for an position with my department and one of the first things we do once we get a resume is look them up on the Internet to see what we can find. It was simply amazing of all the pictures and posts we found! Some things were harmless but others were, let's just say, interesting.
Working with Google Pages was fun! Having another outlet to post and share my professional history is great! I like the idea but being able to as creative or simple as I wanted to be. I'm sure with the way we as a society are heading into more of a technology based future, having sites like Google Pages will make things more convenient and easily accessible.