I'm currently running Ubuntu with Unity - first time after a long time of using Gentoo, Fedora, and then Arch. Unity seems quite well integrated, but it feels limited to me. I still have to configure it to integrate with Thunderbird rather than with Nautilus, and I'll probably install Amarok or MPD for music. I haven't really looked yet, but suspect that it might not be quite that simple to integrate them into unity in the same way that the native apps are.
But I'll probably end up frustrated with the persistent trails of Nautilus and the other natives on my system, and go back to gentoo.