For that application, Maemopad+ is a decent program. It keeps it in a tree format. Only problem it does not sync with anything like MS Outlook and there is no search feature. But you can export the content but I haven't tried it. I like it better than a PDA and much better than a phone. BTW, Maemopad+ like many programs is a free download.

Notes that comes with the N800 is a simple text editor. You can do searches but the organization of notes is what you have to do. Also Notes does not have any kind of sketching feature like Maemopad+. There is another one but can't remember what it is and did not work for me anyways.