I LOVE LOVE LOVE cats in businesses, especially the attention whoring cats that can not stop being up people's asses (sorry, cat allergy sufferers.)

HOWEVER I think the bare minimum if you're going to do this, is to have like an 'air lock' situation, 2 sets of doors so if the cat gets out, it's still not outside. Otherwise, you're putting a lot of stress on your customers to not accidentally kill/lose your cat/s.