I agree with Sas. My cats were introduced one at a time and they all did the hissing, growling thing. In fact Cookie still growls at Tama when he gets to close to her and it's been 2 years since we got him!! It just takes time.
I also get clumps of cat hair on my floor occaisonally. But the kitty fights don't seem to last very long and everybody's friends again.