I've started to notice changes in the carp's behavior after I hook one too. I read in flyfishing for carp that they actually excrete a chemical into the water when stressed that warns other carp and even some other fish. That explains why they'll abandon an area for quite a while after a fish is hooked, but not why they'll abandon it for good.
Thanks for the offer of the flies Quentin, but I think I have all the necessary ingredients. I'll give it a shot tomorrow with one and see if the colors I have are close enough. If mine don't work out for me maybe I'll take you up on the offer. Maybe I could offer a couple of bead head prince nymphs in trade?