I tend to just run what I need on my desktop computer and close apps that I don't. I use my N900 in much the same way.

My use cases/apps are mostly:
1. Browser,RSS and e-mail when catching up with news (and Mauku until it stopped working) and mail
2. many browsers windows when just surfing
3. when out openstreetmapping, Mapper and Camera or if I'm also geocaching then I also run gpxview.
4. notes or maepad when taking various notes
5. media player when walking, gym (watching series episodes when on the cycling trainer makes it much less painfull and a waste of time

Then of course I have plenty of background/desktop applications, calendar, email, weather and facebook, IM networks online, etc.