However, social networks do a pretty good job at segregating - as long as your friends are bourgeois and share your bourgeois design sensibilities, you can use MySpace without bumping into too much 'profile bling'.
Instead, it seems that some white and Asian kids of high socioeconomic status joined Facebook because it was associated with elite universities and therefore reflected their aspirations - and once this process started, people went where their friends were, self-segregating along racial and economic lines just like they do in high school (and throughout the rest of society.) Aesthetic tastes became a socially-acceptable justification for that move, but I don't think they were the primary cause.
That said, a good knowledge of the aesthetic preferences of various social groups could be valuable. Could a startup trigger a similar 'white flight' in an established service by intentionally appealing to the most economically valuable demographic? Can we build good niche businesses by creating things like race-specific Twitter clients?