For a full list of changes, consult the list of tickets and the change log. We fixed one annoying issue where a tag and a category with the same name could get muddled and prevent each other from being updated. There are a handful of contributors to this release, but the one that sticks out is Kim Parsell. She helped to fix a bug where an old picture file needed to be apart from core.
Updates are slowly rolling out and if you are one of the millions already running WordPress 4.1 and your site, it should update within the next 72 hours. If not, visit Dashboard ? Updates and simply click “Update now.”