After I emergency upgraded THREE of my blogs whereon I had the twenty ten theme installed and modified, I realized that my stylesheet had been set back to default. It had been overwritten by the upgrade package of WP 3.04! Now I have to redesign! three websites from scratch.
I did assume that the upgrade package would not contain any theme since that wouldn't be very logic and only enlarge the package and the upgrade time. Now since there is nothing I can do about it and I don't have a backup, I thought I'd first of all, write this here as a warning to all who have their blogs running on twenty ten, and secondly as a 'feature - remove - request' to the developers.
Happy New Year!