Make it possible, when comparing profiles, to look at another user's progress on unofficial lists, not just official ones.
Not each of the thousands of unofficial lists, but have a button on the user's profile page "view his/her progress on your favorite/watchlist lists".

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Life as Fiction commented
Think of it from this angle: I have a few lists where I'm not that far ahead, and I'm curious if there are others out there who have seen more with whom I can discuss the unseen films. A "top users" for personal lists would allow us to gain such insight.
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Lauren Donis commented
You can still do this by typing their username into the URL of an individual list, but I'd like this too (as well as being able to see Top Users for unofficial lists, even if it just included friends). Maybe a little drop down menu on a personal list so you can choose to see the progress of a friend.
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Life as Fiction commented
Similarly, I'd like to see the "Top Users" options for user lists, though I wonder if that would put too much strain on the servers?