Are My Space and Facebook an in the moment fad soon to go the way of the ham radio, or will the user base continue to grow as more and more users are "linked in". I have had the opportunity to join and use these various social networking forums and find myself enjoying them, but each for very different reasons.
For My Space, I find it offers more personal creativity in creating a web page, yet in that disjointed manner, find various pages too busy and hard to read. At the same time, most requests for friends come from strangers with sleazy offers.
For Linked in, I see it as a great business relationship tool to share your CV and learn more about other people's business skills and possible shared professional relationships. As a business networking tool, it is very impressive and has the potential for more business applications.
For Facebook, I enjoy its social networking strengths and its ability to passively share info, thoughts, common interests, and passions. Unlike Linked in which does not need to be updated often, except to add contacts, Facebook requires an increased level of interaction to keep the information relevant and useful. It begs the question, how often are you willing to keep involved, or will one find something better and just as quickly shift allegiances. Facebook seems to be to have the better staying power as it opens itself as a key "home" page for the user to start from in their launch of the web. That means that it needs to add additional features to be regarded as that key portal.