Case in point: OneNote 2010 doesn't have a word count feature. But you can get one by installing the Word Count add-in by Jeff Cardon, who works on the OneNote team.
Before you start, you'll need to know which version of Office 2010 you have installed: 32-bit or 64-bit. The add-in comes with separate installers for both versions. If you don't know for sure, launch OneNote 2010 (or any other Office application) and then go to File, Help and look in the About section off to the right:
There it is: I have the 32-bit version. Now unzip and run the appropriate setup.exe installer:
Now launch OneNote and click on the Review tab. There's a new Word Count button:
Click it to see a report on your word, character, and paragraph counts - and more: