Like several others, I've been keeping an eye on the leaderboards for Winter Bash 2015. One thing I've found annoying is that when people gain a new hat and change position, it's not always clear which hat they've just earned. I can tell their total number of hats has changed, but no more than that, unless I happen to remember exactly which hats they'd already earned before.
It would be much easier to follow the leaderboards if each user's hats were shown in the order they've been earned. Then, for instance, this screenshot
would tell me that Bhargav Rao's hat count on SO had gone up from 26 to 27 because they'd just earned the Living in the Future hat there, rather than having to guess which hat they'd earned most recently.
In particular, this would make it easier to spot new secret hats for those who haven't earned them yet: just go to the network leaderboard and check the top hatters' most recent hats to see whether any unknown ones have appeared.
(I realise it's probably too late to implement this for the 2015 Winter Bash, but maybe something to consider for next year?)