The way i see it is how "I" multitask, and if/how the N900 helps there.

- I walk a lot, hearing music, usually with the pedometer widget activated, sometimes taking photos, or checking the gps.
- Reading ebooks and sometimes hearing music while doing that.
- From time to time loading Grr, opening links in browser and keep reading the rss while those pages load in background.
- Sometimes checking something at google, or a web site (while doing any of those other tasks)
- From time to time checking for updates/new apps.

Of course there are things running always in the background, like mail checking, calendar or even updating the weather,

There are a few things that limit or discourages how much i can multitask with it. There are things that require exclusive access to features, like loading the default camera app pauses the music or talking by phone affecting your data connection. Heavy IO activity affect interactivity/responsiveness of the device, so not try to i.e. play an action game or see a video while installing programs. And battery matters, so i restrict not very essential things for me that could add extra load (i.e. not IM permanently loaded, usually not gps tracking while walking, always having bluetooth off and screen with minimal brightness)