I'd love some feedback on how you're using "Favorites" and "Started'. Our data tells us that while lots of you click "Favorite" on problems, you infrequently go to the "Favorite" page to look at all of the problems you've favorited. The "Started" page has similarly low traffic.
Let's start with "Favorites". "Favorites" can be used in two different ways – to bookmark problems you like, or to tell the author that you appreciate their work. We are considering breaking it out into two separate features: "Like" and "Save to ...". "Like" would be a straightforward way to tell the author that you enjoyed his/her problem. "Save to ..." would be a more advanced bookmarking functionality, where you could create different collections, and organize your favorite problems into these various collections. You would be able to come back to these collections, share them out to others, and browse others' collections. Over time, we may add functionality that allows you to quiz yourself from these collections of problems.
"Save to ..." would also replace "Started", since you could simply save problems that you're interested in coming back to, to a "Solve Later" collection.
I'm interested to hear what you think about this. Feedback welcome!