I enjoyed the demo and discussion around Onenote at the Chicago conference last week.
I mentioned Evernote ([url]www.evernote.com[/url]) to a few folks including Mark and Mike. This is a similar product that works on Mac OS as well. While Apple tablets aren't common, you could use a Wacom tablet or similar with this.
Evernote (previously was a Windows-only "capture" tool to collect web pages, typed notes, images, etc. Their latest beta release is cross-platform (Windows, Mac, web, and iPhone) Your data is stored on the Evernote service, and is automatically synced between clients automatically.
It has basic handwriting recognition as well as text recognition within images, which works amazingly well!
I'm not yet using this for O3's, but thought there may be some more interest in this. I have a few beta invites, PM me if interested.
On a similar topic, I thought I'd mention Highrise ([url]http://www.highrisehq.com/[/url]) from 37signals as a great one on one tool. Highrise is intended as a CRM-like tool, but I've found it great if I enter directs as contacts. There are spaces for keeping personal information handy (great for recording kids, wives, husbands, pets, etc names and the like) as well as on ongoing diary for each contact. Finally, there is a reasonably good task list function that allows tasks to be associated with each contact. I can also keep annual goals and development plans linked within each contact.
During one-on-one's, I take paper notes in a notebook, and then transcribe the key points and action items into Highrise. Highrise has a great search function, so if I ever need a future reference, I can search there, find the date of the conversation, and then refer to my paper notes for that day.