Just wrote a Tomboy add-in allowing the user to keep notes in Tomboy notes. The idea? If just like me you rely a lot on short tags such as TODO or FIXME, you find it convenient to have the editor highlight them. It is exactly what the add-in has been designed for.
Mandatory screenshot:
Editing notes with FIXMEs and TODOs.
For more info and downloads, have a look to the Tomboy-Todo project's page.