Not for the vast majority of OS X users. Sure, many of the tech-savvy Mac users I know use it, but none of the laymen do. And it's the laymen that Apple's primarily targeting, because they're a much bigger market and much easier to satisfy.
Not necessarily true or they would have stopped shipping things like the terminal.app a long time ago (or including python, ruby, etc.). Even apps like Automator are probably out of the scope of 'laymen'.
I only use it as a cheap way to mentally background apps that won't be looked at as often (e.g. iTunes, running a server in Terminal).
I find that the focus model tends to break down in Spaces for any multi-window application like Finder, Chrome, Emacs and Terminal. If every window of an application is going to jump to the top then that just adds extra work to switching desktops.
That being said, I do like the Application->Window switching model on it's own and wouldn't trade this for Virtual Desktops.
