I have a 3Com (3c589) PCMCIA ethernet card. The 3c589 driver for Amiga specifically mentions needing both CardPatch and CardReset in your S:user-startup for it to work. I did what it said and everything works fine.
I suppose it depends what card you're using in there... my PCMCIA Compact Flash reader for example worked perfectly without any changes to the PCMCIA system.