Wordpress MU allows you to create a network of blogs. Normally, search engines treat sub domains as seperate domains. But what about Wordpress MU? Do the search engines this that all of the blogs are coming from one domain or from multiple domains?
Well as long as they are in a subdomain and not in a subfolder, then they should be treated as a separate site but I'm sure there are parts of Google's algorithms that associate the authority (not page rank) of the domain with the subdomains, but I have nothing to support this theory.