Office Online Blog recently published an article from Bill Gates where he explains how useful is Office for him. The most important tool for him is Outlook, but look what he says about his Tablet PC and OneNote.
I always take a lot of notes about ideas to think about or things to follow up on. I try to bring my Tablet PC to meetings as often as possible so that I can use OneNote 2007 to write notes in ink that can later be searched or converted to text. Even if I forget my Tablet, I can scan a document or piece of paper and add that image to OneNote. One of the nice new features in OneNote 2007 is that it automatically recognizes the text in those scanned documents, so that it's easy to search for them later.
I love OneNote too.