Yes, just as if I like Pearl Jam, I'm likely to like Soundgarden.

But my point is that both of those judgements are based on coincidence, not musical similarity. Fifty years from now, someone might be shuffling through the oldies section of their local Ogg Vorbis store and pick up some Pearl Jam on a hunch and decide that they like the band. The chances that they would also like Soundgarden are not, I think any more significant than if they might like Iron Maiden, based solely on the fact that they like Pearl Jam.

The reason that a lot of people like Soundgarden and Pearl Jam is because they were part of the popular music culture at the time in which both bands were popular. Outside that coincidence, they bear little resemblance, and a suggestion to one based on the other is likely either to elicit either an ``I already know them'', which doesn't help, or to suggest another artist which has little similarity.

Replacing those two artists with Eminem and Britney Spears just exaggerates the issue.

Say your mom is playing on the radio and hears a Britney song and decides she likes it (for whatever reason). Is she likely to also like Eminem? I doubt it. The only people who like both like them because they're currently popular at the same time, not because they have any relevance to each other.

The point of a music suggestion algorithm is to provide suggestions to people based on what they currently like, not on what happened to have been popular at the same time. The only people to whom that would be important are the people who are already aware of both artists, and to whom, necessarily, such a suggestion would be irrelevant and pointless.

Sorry to say the same thing over and over. I can't quite figure out how to put it in words properly.