In the past I felt that Google Sites (ex JotSpot) would follow that route but it seems it's now in the limbo.
(EDIT: cancel that, I'm an idiot. I just found a big honking "Find Tags" button right on the main ribbon that I'd completely overlooked before.)
I never understood the appeal of storing the entire freaking notebook in a single file either. When I started using onenote, I used the webcam recording feature as a sort of video diary, and this completely broke down my backup scripts (I put everything on amazon s3, which doesn't support diffs.)
/ end rant
Back to your comment, I don't quite understand what you mean by the online spreadsheet integration. Could you elaborate? I mean, the contacts integration with Outlook is pretty cool, but is virtually useless with anything else in the universe. What is the advantage here?
Look at the bottom of the Tags Summary panel when you click on the "Find Tags" button. You should see a "Create Summary Page" option. It's a great way to create summary/wrapup's of meetings and projects.
What I tried to say with integration is that you can read from external sources and put the information in OneNote automatically, you need to build some add-on or connect from a scripting language to do that.