UX designers are scary IMO. Often they have totally different ideas about a good desktop environment than the rest of us. Might end up annoying lots of your users (Firefox) or even breaking it for a significant chunk of your userbase like Ubuntu did when they decided to imitate a certain fruit company. (Yep, between moving window controls, messing with the menus, breaking alt-tab just the same way as said company and even adding a dock, thats what they did.) Certain users like it, others like me left.

Edit: the thing it seems they don't understand is:

Firefox: the people who prefer Chrome already use Chrome or Chromium. We use FF because for some reason or another we don't like Chrome. (For me, that is extensions.)

Ubuntu: lots of us used Ubuntu because we really liked it, not because we couldn't afford anything else.