I don't touch my fish, and try my hardest to keep my hands out of the water. The smallest amount of soap, lotion, ect on your hands can do major harm to the fish. Touching them will also remove the slime coat from the fish and that leaves them prone to sicknesses.
I have been cleaning out my oscars tank before and if I have to put my hand in the water he will come up and rub up against me. I don't like that he does this, and I will put meds in the tank with him to help him with the stress coat.
Before I clean my tanks I always wash my hands, just with water, no soap. This helps take off all the stuff that can be harmful off my hands.
Contrary to what some have said, I don't think it is good practice to touch your fish. It most certainly can do them harm, doesn't mean it will, just that it can, and I don't want to take that chance.