One thing I'd love to have fixed is the shaky support for various bluetooth headsets/carkits. It's been bothering me since from the beginning. None of the Nokia PR's would make any kind of improvement or difference at all.

Is that the kind of functionality that the CSSU team would be able to do anything about, or is this closed Nokia source?

Anyhow, I think that many headsets and car handsfree units has appeared having the same trouble when connected to the N900, in my case, an SE HCB-108 it does connect, but the sound is so terrible that it's useless (it's robotic voice some strange acoustic feedback and dropouts all the time).
I have tested my car kit with other phones without any problems.

This was one of the bug reports that discussed it:
https://bugs.maemo.org/show_bug.cgi?id=6766