I agree: it should be a great addition, but it hasn't really been used to advantage. I think the main thing is that it needs some publicity: many people have never even noticed it. I've tried to use it for comments, but it's hard to be diligent if no use of it is ever made.

Another easy thing to do would be to add "Most Favorited" to the "Lists" page. Maybe it would be possible to show the number of favorites that a post or comment, with a reverse link to who has favorited it? Maybe add a notification to the creator of a comment that is favorited?

Possibly instead of just having a link on people's profile page, you could have a rolling list of the their most recent favorites? Or maybe for "person" discovery, you could automatically show who else has else favorited something after you do?

It seems like a good feature to start publicly experimenting with. Announce something, try it out for a week, then post a thread asking people what they think and how it can be improved.