I have been specifically looking for ways that my UX and graphical designer friends can get involved in Free Software, both because they always seem to want more portfolio projects and because Free programs tend to have questionable UX.

It's not easy. A user interface is not an easy thing to change, so unless a developer consults a designer from day 1 (or has their own design chops), the application could be stuck with a suboptimal user experience for a long time, ultimately limiting adoption to geeks, hackers, etc.