Would I be using Ubuntu if it was as popular as Mac OS X? I don't think so. Part of the allure is the geekiness.
For me it's about having the apps I want to use, good cut and paste, and better updating tools.
I use Ubuntu because it's good. Not because it's obscure.
... same reason I use Windows. It's got the apps that I want to use. I could care less about the operating system as long as it's not running on a Mac.
What's wrong with a mac?
It's more expensive.
It's incredibly stable. And a polished, supported, user-friendly end product.
Ubuntu might be already as popular as Mac OS X, and we just not aware of this.
I personally, passed over my macbook after three months and grabbed ThinkPad with Ubuntu.