As a result of M750s success with pyOBD
http://talk.maemo.org/showthread.php?p=1142233

Carman is now connecting semi-reliably to my BT dongle.
I don't know whether it's
1. Setting the N900s Bluetooth config to "Visible" (which isn't necessary with some other BT devices I've used with the N900)
2. Or something pyOBD brought with it.

At any rate, if the N900's bluetooth config is set to "Visible", after starting Carman and getting past the internet connection nag, go to Carman's OBD Connect. It will fail the first time. And then it always connects on the 2nd attempt so far.

Carman is still messy: problematic nag for internet connection when the application starts, whether you need internet features or not at the time; GPS remains ON regardless of previous GPS state after Carman is closed, using battery; who knows how much it's leaving behind & burning battery when shut down; etc. But (for me) it now can now be expected to connect.

Carman's better suited as a limited driving tool, but pyOBD is a better diagnostic tool (& less messy).