Hainvg a look at the firmware download site:
http://tablets-dev.nokia.com/nokia_N900.php

It seems I can get three different versions of the firmware. A global version, a USA version (002) and a Middle East/North Africa version (003)

Looking through the packages on my device I appear to be using a "203" version

dpkg -l |grep mp-fremantle-
ii mp-fremantle-203-pr 1.2009.42-11.203.2

this doesn't appear to be available on the download site

What regional versions are people running?

I'm reluctant to reflash with a global version as I can't seem to find out what the differences are and something might be important (like partial ALS/line-2 support which didn't work on a generic device I saw a few months back)

I want to start ripping my N900 apart, testing and developing bits and pieces, but I want a good "undo" just in case

I'm guessing this might be important for other regional or country releases? How many different versions are there?!