I use it for everything! Work Projects, diaries, manuals, task lists and meeting notes. It feels great to be able to off load my thoughts onto OneNote. For those with busy lifes, I highly recommend a concept called Getting Things Done which is a way to organize projects, big and small in your life. Combined with OneNote on windows phone and on a windows desktop, its a complete life changer.
I think my notebook has over 500 pages.