The N900 has a great screen, but the calendar doesn't use it properly. E.g. in week view I can only see the first few hours of a day (0.00-4.00 in the morning/night) because some day items were synced as items at 1.00 or 2.00 o'clock. So oterh items during the day are not visible at all, you have to scroll.With an improved week view this wouldn't be a problem
Better calendar views like a Week grid view (eg like your filofax week view, as implemented in e.g. Handycalendar and Papyrus/Calendar for Symbian s60, or like the old Psion Agenda) should be possible and would greatly improve the use of this program.
There is space enough on the screen ad the resolution is big enough to allow for such views.