Excellent virtual world consultancy Kzero have a site with some interesting content. They are the people behind the Second Life Brand Map:
A Metabrand is a brand that is created to exist solely in a virtual space. It lives only on servers, is powered by electricity, experienced only on a computer screen and serves to provide a service, solution or product to avatars living in a metaverse. A Metabrand satisfies a demand that exists purely on a virtual basis.
Post explaining metabrands: http://www.kzero.co.uk/blog/?p=717
First metabrand case-study: http://www.kzero.co.uk/blog/?p=752