i've seen people walking their pet dogs in walmart a few times, but as long as they are not too close to any food, leaving their waste behind, or bothering people, i really don't mind. i just don't want to step in shit at the grocery store or see a dog hiking it's leg on the fresh produce
also, it does depend a lot on which store or other establishment they are in. for example, it would really irritate me if i saw a dog at olive garden or chili's, but dogs in petco (obviously) or game stop wouldn't bother me a bit
edit: any dog that barks excessively bugs me, but in a store, it would make me want to kick that dog in the face.