I've seen a reaction to Porthos, but only good words about Archer himself.
I like Porthos, I think it's a clever idea for different kinds of stories (I have changed my mind on this.)
I liked the scene in 'Cold Front' when Porthos is concerned for Archer's wellbeing. A cat could never react like that. Data's cat, Spot, was only used to bring elements of Data's character out. I would like to see more of Porthos.