Researchers at Parks Associates say social networking users are not loyal, citing stats showing that nearly 40 percent of MySpace users keep profiles on other social networking sites such as Friendster and Facebook. Loyalty among the smaller social networking sites is even lower, with more than 50 percent of all users actively maintaining multiple profiles.These trends highlight a peculiar aspect of the market for social networking services, say Parks Associates researchers. Nearly half of all social networkers regularly use more than one site; one in six use three or more. The result is an increasingly interlinked environment tied together by links, widgets, and the users themselves.
I'm not sure I think this "lack of loyalty" is a problem. Communities aren't federated because the people you know are not all federated. It's just like IM systems. Not everybody uses the same client, so one is forced to use multiple clients, or a client that federates all the clients for you. Social networks are no different.
And of course smaller site users are on multiple sites. The problem with smaller sites is that no single smaller site has lots of people you want to stay in touch with as members. The point of registering with any smaller site is that somebody you might want to stay in touch with might join that particular site and not the others you are a member of.
