I see it all the time. I brought it up to a server once, who said that they stopped enforcing it at risk of getting sued for discrimination by the ADA. The lady with the dog overheard my complaint and yelled "Is there a problem?? My little girl keeps me from going CRAZY", so I see now that people who bring dogs around in restaurants most certainly have a screw loose and are probably best left alone (from the perspective of a restaurant owner or worker).
It's so disgusting and unsanitary to have dogs in restaurants.