Nokia N900 Maemo 5 PR1.2 update -- conclusion

First of all it worked ok!

I did not have enough free space on '/' (root) to complete it at once so it aborted twice for me ..
If it does that: don't panic .. in the terminal (as root) run dpkg --configure -a (which will finish setup of all the already installed packages -- which will clear up more space again. (running 'sync' is always good as it can give u even more space :D

after that just re-start apt-get dist-upgrade ;) -- rinse and repeat until done :d

one thing that caused me trouble for quite a while: All communications logs,.. not working (ie no Call history, message history, .. -- also new messages are maybe displayed if you click on the notification, but if it's more than one it won'T work properly and you will loose sms/im/.. data
This was caused by me getting a SMS when the upgrad eof the comms app was running -> messed it up .. restoring backup failed again due to the same SMS getting delivered again (the last sms seems to get stuck somewhere in the system -- /var/spool/...)

The solution was simple:
1) Put phone in offline mode
2) restore a backup which you should've done before even starting to attempt an upgrade like this
3) put phone in online mode again
---> works again :D