Just got my iBook back from the shop today.
Yep, the previous logic board substitution solved the problems I had but gave me a whole set of new ones.
Still I have to commend Interlog (again) for letting me keep my Mac while the new logic board was en-route (which only took 2 days this time around) and then replacing it from 18h00 one day to 9h30 the next day.
Way to go, really!
Now I just hope this board is actually fully working…