I just managed to get my first level up in Darkness.
Now I remember reading somewhere (propably in the SIM news) that assigning skill points is possible, but it's buggy and not save.
Does this still apply? Or can I assign my skill points without danger?

You can assign them without danger (from the Manage -> Character screen on the menu). However, be aware that not all skills are fully defined and some may change before the Combine is finished. Assign skill points at your own risk, and don't complain later if you realise you wanted them on something else.