Yeah, I use OneNote constantly. Sorry my first post was so short, but I guess I just assume everyone knows about it. Definitely a tool I can't do without.
You can create & edit notes on your WP7 phone, a desktop/laptop, the ipad or even the live office web app on Skydrive....and in any case, it will sync with Skydrive, and in turn, sync with all the above mentioned devices.
Of course, for the desktop, you have to have Microsoft Office. I don't know about the iPad app, but the web version is free, and of course, the app is included with WP7.