I love my 2 ferrets so I can't say there is any cons, the only one I can think of is that some seem to have alot health problems. I haven't expereinced any with my two though.
The pros are that they are amusing to watch and interact with, they hide anything they feel like hiding, my one drags my shoes around the house and hides them.
I guess if you have a sensitive nose the smell might be con as well, but I don't mind it at all.
There is probably more information that I am forgetting about, but I am sure that others will chime in.