I've seen people apparently use them to reasonable effect though, so I'm going to assume that people capable of note-taking on mobile are just a more evolved kind of human than I am :-)
In paper, I tend to really note-take. I like note-taking on paper for things I don't really understand yet. I prefer pre-writing in an app for situations where my understanding of the topic is good, and I want to skip steps (e.g. writing a blog post about a presentation, where the topic is already familiar)
Now, in fairness, I have recently started using SimpleMind for mind-mapping real-time. I find it does a good job at doing both things. It helps me build a narrative structure in one branch, while capturing notes in others. It also gives me a lot of nice flexibility on-screen to rearrange branches, relocate topics and do other general house-keeping.
Sometimes I'll capture to paper even if I'm sitting in front of my computer. If I've got something complex to reason through, I like the free-form nature of paper. I pretend it's an auxiliary scratch buffer whose contents I will reason about later.
My paper notebook, therefore becomes pretty nonsensical, because it isn't the system of record. I carry it as a notebook because I can always go back a day or two if I got lazy and didn't transcribe the previous day. Also a paper notebook puts on a better show for society as compared to just having a few sheets of printer paper along for the ride at meetings (though that works too). Periodically, I rip previous pages out (if spiral bound--they tear cleanly) and shred them just to restore that fresh notebook feeling.