Ubuntu's website shows of its Dash "Spotlight", Launcher "Dock", Status Icons "Menu bar with status", Workspace "Spaces", Ubuntu Store "Mac App Store". It's almost like they're trying to directly compete with Mac OS X, with "killer features" that match exactly with what apple regularly shows off with Mac OS X.
I'd love to see some data one way or the other, but in my experience and among my friends and associates, people who buy Apple computers are incredibly likely to value the polished, "just works" factors of OS X and if they do care about being UNIX-like, it has them covered too. Then among those who run Linux as a primary OS, they do so without paying for the shiny Apple hardware. Again I stress this is a personal subset and I welcome it being corrected or confirmed by hard numbers.
At the same time, perhaps I am looking at this the wrong way: If you have a goal of being the best desktop experience, then better to pit yourself against the best?