I wonder how hard it is to write such a daemon - does anyone here reading this an idea how to get started with this?

hm... whereas... two question are raising:
1. does google provide an interface to fetch the data from the google calendar & contacts
2. is the nokia n900 capable of to differentiate between these entries? so, do we have support for multiple calendars? if not, you could write a daemon to fetch the data from google calender, but with the next exchange sync all your private data will be on the company's server...