I just saw that there have been a couple reviews of OneNote 2007 that just came out. The first is from Paul Thurrott and his SuperSite for Windows. You can see the review here: Microsoft Office 2007 Review Part 3: Office 2007 Applications. Here are some of his comments:
And as fans of the previous versions of OneNote (2003 and 2003 SP1, the latter of which was a major upgrade) might expect, OneNote 2007 is a winner.
What we do get this time around is a bunch of evolutionary improvements that make OneNote feel like a much more mature application.
As implied above, OneNote now supports multiple notebooks (finally). This allows for further levels of organizational opportunities and frees users from the folder-based organizational scheme required by previous versions.
OneNote picks up the Instant Search functionality from Outlook. I've never been a huge fan of the way OneNote searches, but at least now it's quick, and you can search across multiple notebooks.
I was in love with OneNote the second I saw it, but as a heavy user, I've also developed a wish list of needed features. Some have been answered in this release (while others, like notebook locking, which could prevent future edits or deletes to archive notes, have not). One is in-note hyperlinks that link to notes elsewhere, be they in other notebooks or folders, other drives, or PCs, or Web locations. OneNote 2007 adds this useful feature, allowing you to logically jump around notes in a way that's been available in hypermedia solutions since the late 1980s. Back and Forward buttons in the Standard toolbar work just like those in a Web browser.
OneNote is a misunderstood application. Although some people think it will only work on a tablet PC, this is far from true. OneNote will work equally well on a desktop PC, notebook or a tablet. There's even a pocket version for use on Windows Mobile devices.
At its heart, OneNote is a place where you make notes, scribble diagrams and gather information. It's quick and easy to jot things down, paste stuff in from the Internet or other applications, then drag it all around and share it with other people. If you do run OneNote on a tablet PC, you get the added advantage of being able to handwrite notes and later have them converted to text.
If you store a OneNote notebook in a SharePoint document library or network share, all of its contents are available to anyone with access to that document library or share. Email someone a link to that notebook and they can synchronise their copy of OneNote with the shared notebook. They can then make changes, such as adding, editing or deleting text, graphics, pages or sections, whether they're online or offline. Any changes they make while offline will be replicated on the server copy next time they connect, and OneNote will automatically resolve most conflicts by itself. If you don't have a central server, you can share a notebook directly from your PC.
OneNote is a fantastic application that deserves wider attention. It's now included in the Home & Student, Enterprise and Ultimate editions of Office, but users of the other editions should seriously consider buying it as a separate application.
And one last thing from Simon's review: