Yes, Ubuntu is fairly active in the UX field. Here are a few links for your reference:
Ubuntu Design Blog
Design team at Ubuntu
Design Research at Ubuntu
Launchpad project that tracks all user experience (UX) bugs related to Unity Next
UX design jobs at Canonical
Even though I have never been a part of their UX design community, I can vouch for Ubuntu ...
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Seems like a sensible thing to do with your time, well before you do the things suggested in Jørn's answer, is to first ask the project developers if they want your help. Specify what your expertise is, and what you can and can't offer. If the devs don't reply, aren't interested, or are too arrogant to accept criticism (not that common, but it does happen), ...
Have a look at this Boxes and Arrows article:
The challenge with teams, large ones especially, is to promote holistic understanding of the project. The article argues that the quality of the project and the user satisfaction is influenced consistently by how invested and informed each ...
These would be hidden features so you need to think about learnability.
Some might argue that these are to support your super users, but even they would need to learn about them.
Some UX people could argue that for every hidden feature you should provide a visable alternative, e.g. vie a menu, etc.
however, you can consider using an Onboarding interaction ...