My kitchen cabinets are in good condition. I want to paint over the oak finish. Do I need to sand them first, or would a good scrubbing with a teflon sponge be enough?
Both a good washing and sanding is needed. The washing is to remove surface contamination before the sanding and roughening up the surface with 120-150 grit sandpaper will increase adhesion of your primer.
At this point it is best not to skip any part of the prep. Washing and sanding is the foundation for the primer and paint.