suninmyeyes: The early Cessna Cardinals were tricky to land and there were a lot of pilot induced oscillations. Cessna redesigned the stabiliser and put slots in the leading edge to make it easier to control. This was retro fitted free of charge to the earlier models which suggests it was more than just a nicety.
Part of the problem was most Cessna pilots transitioning onto the C177 were not used to the fully flying tailplane which was much more effective than the traditional Cessna elevator, this contributed to the PIO's.
The early tailplane could also stall before the mainplane causing issues which were addressed by the leading edge slot.