We're talking about Digg doing this as a differentiation. It is not commonly used because it is very heavy in IO and CPU for individual users (though a site like reddit could take a shortcut just by periodically ramping up some spot high CPU instances and batch generation correlations between users on every subreddit, then staling that until the next run), and sites like Reddit and previously Digg ran on stacks that greatly limited their ability to scale for this.

Regarding music taste, if the system knows that you have a strong correlation with a number of users who like classical but periodically explore new music, what they like will likely be something you might be interested in. This, in practice, is exactly how music discovery happens in the real world (that the discoveries of the people you share musical tastes with are more likely to interest you).