So... joerg_rw was talking about tweakr today, and how it just replaces values in the general profile.

I looked into profiled, and apparently, the N900 can support more profiles, it pretty much had support for it from the start!
Unfortunately, the UI team decided general and silent were enough, so you can't add profiles easily.
I'll look more into this (it seems to be fully working, different ringtones for different profiles etc), but it needs a UI rewrite of both the status bar applet, AND the control panel applet.