Love my cast iron. And I'm with Irwin on this one, there's nothing wrong with using a little soap in a well seasoned cast iron pan.
When still breaking in a new pan (or one that's in need of new seasoning for some reason) or for light clean up, I wont use soap. But for a well seasoned pan there's no harm in using it. Soaking, especially in soapy water, is liable to screw it up, but a few drops of soap and a sponge aren't going to hurt anything. Salt will help with crusty crap, but not grease.
As for eggs, I never have a problem. Right heat, little oil or butter, and proper amount of time before trying to flip or move them around.