I think that the success of Facebook seems to depend upon its viral effect. You can invite your friends to see you inforkation of all kinds, you pictures, your interests. There are many gadgets to enable you to do this and they are increasing all the while. Almost all the things that can be shared on my other thirteen sits can be shared on Facebook
There are many sites like Plaxo, Linkedin and MySpace that enable you to link up with people all over the world. If you are looking for a job, put your cv on Linkedin will help you. For professionals the site called Plaxo may be better. If you are looking for a partner then try Adult Friendfinder.
In Facebook you can share everything but it has come rather low down in my list of top sites, because it caters mainly for younger people, I am also rather shy about sharing everything. It has recently been revamped. You can be clearer about how you are meant to be in control and what risks you may be taking.