I fairly often install Ubuntu on clients' machines, and haven't had any complaints about it yet. I have a few small businesses using it exclusively or nearly-so, and I've installed it on many residential clients' kids' machines, as well as on a lot of machines in child care centers and schools. The kids love the games, there's plenty of free (and excellent) educational software, and the systems are practically bulletproof as long as the kids don't have admin privileges. It's also easy enough to administer that a reasonably savvy adult can be taught to do all the routine stuff.
That's how my goddaughter got so good at doing the installs. She would do the Ubuntu installation, and then use Synaptic to download and install the zillions of games and educational apps, and finally teach the adult users (or older kids) how to do updates, install and uninstall software, and so forth.
It's far from perfect, but Ubuntu is about as close to being ready for the masses as any Linux distro out there. I'd say SimplyMEPIS is second (and probably has the edge on Kubuntu for those who want KDE). But I still use RHEL on my Web servers because it's the best distro, in my opinion, for that purpose; just as I still use XP for Web development, despite having Vista and Win7 machines available, because XP is what runs my preferred development tools best.
So sure, Ubuntu's not everything that some zealots make it out to be. I could say the same about any Linux distro I've used (or any OS I've tried, for that matter). But with the possible exception of SimplyMEPIS, I can't think of a Linux that I'd even consider suggesting as an alternative OS for the average Windows or Mac user.
-Rich