It would be helpful to be able to create fields with per-user values.
For example, I have a playlist that needs to be reviewed by multiple people. I'd like to create a field per playlist that the user can set that marks it as "reviewed?" This can be a simple checkbox, but the value should only apply to the current user - for them to keep track of what they've done (similar to how a note can have the status "read" after a user looks at it) without affecting another user's "reviewed" status.