Pandora, bookmark songs and artists

Pandora is allowing users to bookmark favorite songs and artists.
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This is incredibly powerful - not only does it add a lot of value to the users (obviously, and very late in coming), but also in the wealth of data that Pandora can mine.

Earlier, all they had were thunbs-up or thumbs-down marks that a user could give when a song played on a station, thereby helping Pandora's algorithms in refining the station. Now there is a second level of preference available - which songs, among those the user already liked, does he/she like enough to bookmark for the future?

And as an aside, there is also the more plebian opportunity to ask users if they want to buy these songs...