Actually, that gives me an interesting idea. I normally read on the bus during my commute. Mostly I read ebooks or websites (still working though the Sequences), but I've slipped the occasional e-audiobook in there too (tip: get them from the library, way better than "buying" a DRMed copy). There's no reason I couldn't take notes on my phone while listening to an audiobook. The playback controls are in easy reach, so I can pause or skip in either direction quickly, but at the same time I can have a note-taking app (I use OneNote usually, but there are lots of options) open. If you've got decent typing speed on the phone, you can probably even manage with minimal pauses in the narration.

Some e-reader apps will let you take notes on a text as you read it, but in most cases those aren't nearly as easy to review as OneNote/Evernote/whatever and you still have to take time away from reading to write. Audiobooks don't have that limitation, so long as you can take notes on the last thing you heard while still listening at the same time (a skill I mastered during a particularly intensive course back in freshman year).

Of course, none of these options work very well when walking. I'm not sure what would, aside from stopping to pull out your device and put down some notes.