Original post was not public because you don't tell your current employer about interviewing at other places. I've changed employers since, so it's not a secret any more.
Back in October I applied for a product-manager job at Stack Exchange. After the phone screen I was given a design problem: the pages on the site that describe privileges (which are earned through participation) are widely held to be weak, so what would my redesign of that look like? I was asked to send a sketch (low-fidelity; I could take a photo of a whiteboard for all they cared) and a brief explanation of the design choices I made.
I was pretty proud of the design I came up with; I thought it did a good job of not only addressing the known usability issues but fitting into the overall scheme. I identified particular, speculative elements for user-testing. I pointed out issues we were not addressing (which I had confirmed were not being asked for, but you always document these things anyway).
A couple days later they told me they had hired someone else. I had always understood that to mean "bad timing"; I think the only way that could have happened was if their offer was already out before I got past my phone screen. (And that's totally cool; until you have an acceptance, you don't have a hire and should not drop other candidates.) So I assumed it was just bad timing, but I never got any feedback on my design, so a part of me wondered if I had flubbed that.
Today they updated that part of the site (just on one of their sites so far). It looks, ahem, familiar. (Sadly, the Internet Archive doesn't seem to have a "before" view.)
Oh good. That makes me feel warm and fuzzy.