I thought I should revive this thread. I now have 2000 km on my Gazelle Ultimate C380, and was always disappointed at how stiff the ride felt over bumps. I felt that the front shock didn't really do anything... and I was right. After looking at this thread a few days ago, I went for a ride and tried to bend to the side while riding to see if the shock was actually moving. To my surprise, I saw that the boot around the shock was compressed all the way, so the shock was basically bottomed out.
I followed the adjustment instructions in the Post-Moderne Unicon manual, tightening the spring tension by several turns over two tries, and the difference is like night and day. After the first try at about 5 turns, I could feel that the shock was working, but when I bent to the side, I could see that the boot was still compressed almost all the way, so I added more tension. It is difficult to say exactly how many turns of the tension screw I actually made, but would estimate about 10 (I am about 210 lbs). I could feel the tension tightening up as I progressed, starting from almost no turning resistance on the adjustment screw, to slight resistance, to moderate resistance.
As mentioned above, it is necessary to remove the wheel and front fender to access the adjustment.
The Post-Moderne manual for the Monoshock states that the spring tension is set at the lowest preload setting from the factory, and my LBS did not even mention the adjustment when I picked up the bike. The maintenance manuals I could find for the Gazelle do not mention the spring tension adjustment, so I wonder how many Gazelle bikes there are out there with a front Monoshock that isn't adjusted.
If you own a Gazelle with a Monoshock, you may want to check yours.
I have attached the Unicon manual since my antivirus reports the link posted above as having virus threats.