I use Onenote ( beta 2007 ) a lot from day to day. It's a perfect application!
All my school notes are inside onenote.
While I sometimes have some fights with it, because it doesn't always understand my brain. But most of the time it works oke enough.
I would not use an online variant of onenote.
What happends when I am in a room with no wireless?
How good will the audio recording be on an online onenote?
How large files am I able to quickly paste into onenote?
The application just always need to work, just like paper. To archive this in an online envoirment just sounds way more difficult.
Things like the task list intergration with outlook, which I like a LOT! Might be possible, but search, quicly access audio/video or other files is needs a faster connection than availible.
And why should they put massive power machines to host the application, while most tablet's/laptops are not short in power.
I use onenote both in class in "tablet/pen mode" and to take notes from the study books/material by keyboard. The intergration with outlook is just so cool, I can get my to do list in the morning and it auto synchronized with onenote! Click task done, and it synchronized in both!
Being able to work with a group of people on one page with all there own laptop/keyboard is also great for group fights/work

The full screen writing button in onenote 2007 is also great, just gets away all the crap quicly and makes space. While it is back again with a click.