Now , I envision it as being one of the super handy things that Ubuntu has , so bare with me . I've always had trouble keeping track of my daily notes, but I'm frequently around the computer .So when I'm on the computer I want to be able to easily check what the notes/events for the day are and to check them or add more (for any of the upcoming days) .The most handy thing to have is to click on the calendar , which will drop a two-thirds-of-the-screen type of panel (picture : http://dl.dropbox.com/u/42681910/Calendar%20blueprint.png
) , that has the calendar , and in each cell (representing a day) there could be events/notes , that are readable as soon as you expand the applet (and everything hides on Esc or click on the indicator) . I think no other OS has anything similar . So to add an event or to edit one - just click on the cell .
An addition to the idea is to have the cell ,that's clicked on, expand (makes it more usable when there's many events/notes) as shown in the picture.
What I've drawn is pretty bad , but I guess you could imagine a better coloured version with some transparency and some simple open-animation .
Importing/exporting with a mail client and/or Ubuntu One will make the integration complete and enable syncing with other devices through the already existing systems.