Well, having more money means that you can pay more people for working on the project, so I think it does have an indirect influence on the quality.
What has Ubuntu's paid Developer's done? Lets see, there is a new message system but it is broken already.... They have changed the shutdown dialog three times now, not exactly revolutionary. They added a tab for Compiz, too bad Compiz needs turned on and off for games, videos, etc. Again nothing to get excited about. Lets not forget Computer Janitor, the app that wants to uninstall the things you add and doesn't clean anything. I am glad our unpaid Developer's do not follow in those footsteps!
I honestly can't think of anything Ubuntu has done that is really that noteworthy.