if the 2010 notebook is shared to web copy (skydrive),
and you wish to have a local back up copy,
then the only way I've found is to manually save a copy (save as) occasionally locally.
Otherwise I haven't found way to also sync to a local copy.
(Onenote must have a local copy someone because I can use it offline also, perhaps in app data somewhere?, so it should be recoverable somehow)
This is for those who don't like having all their note data stored on the web and want to know there's a back up should Skydrive take a dive.
For One Note 2007 users,
Live mesh will only save a copy to your 'device' folder on the skydrive if you try to be more old school, which unfortunately is not accessible from your mobile via Micrososft apps (for those trying to sync Onenote accross their pc and mobile through skydrive.
Also, to sync to mobile, you need OneNote 2010 (2007 won't work).
Hope that helps someone.