A very interesting post.
Im a noob, and Im not a developer, and Im interested to know how you would like to divide things up for the better.
There is and will be alot of noise, but dividing things up will not stop that happening. The n900 forum will take a on a life of its own whatever happens.
I am aware of the developers forum, have even posted in it once or twice, but tend to stay away from that side of things as it isn't where my main focus is right now. If I start to code, then I will be more active there, but for now the n900 forum is the place for me, for questions, advice and general shared community feel - check the MPD thread

I think that my experience will be a typical one, and I feel happy to start any thread about the n900 that I want, the forum will police its self with the help of the mods if needed. I think that maybe after the xmas holidays it might be time to step back and take a look, but for now, lets wait until more people have the device and see how the forums are being used before making any changes???

The XDA forums are a good example to use, but I think that if there is any learning to be done, then maybe that would be for Nokia, but the situation here is different.
XDA has a huge following for supplying cooked ROM's for phones, filling a gap that the manufacturers have so far refused to do anything about. I'm running WM6.5.3 on my i780, Samsung won't provide software updates to do this, so I went to XDA to get it. The n900 is far more open, so the prime driver for these forums is going to be different, and I think we will see this over time.