Plaxo and LinkedIn are very good networking sites. You can put all your information on there for your contacts to see. This will allow their contacts to see the information as well. And it will go out to anyone that you release it to. Like with the other social networking sites, these sites will make you known all over the world on the professional side of things. You can update your resume, qualifications, experience, etc. on a daily basis. It updates you on anything that you may be interested in. You can search for jobs by category. Just a real good place to promote yourself professionally.
If you had your own website, I am sure that you could make your resume look really good, however this has it set up for you already and you just enter in your material. Also, I am sure that plaxo and linkedin have protection software.. (hopefully) and i am not so sure how you would set this up on your own page. Identity theft is a major problem nowadays, hopefully these information sites will not add to that problem
With everything going online, I imagine this will be the job market type sites of the future. Really cool stuff.