iTunes for Mac? Yes.
iTunes for Windows? Yes.
iTunes for Ubuntu? No.
This is probably the single biggest app missing from the Ubuntu playbook. If Apple were to make it available for Ubuntu, would people really not buy Apple computers? The answer for some would be yes, but I'd venture to guess it's a very small number of people that would base their computer buying on it alone. More likely, it's people like me wanting to put Ubuntu on a Windows box or netbook but find the lack of iTunes makes Ubuntu not as attractive an OS, especially since Apple uses iTunes to sync with the iPhone and iPad.