yeah, I have heard of these guys being pretty aggressive. I know a guy who had one, and it chased his texas cichlid around until he decided to give it away, and the pleco was a good 3" smaller than the tex!
My cousin has one in his 55 and he is very docile. He is a big boy and about 2.5 almost three years old now. About 11" and he is the nicest fish ever....