With the dramatic increase in people attempting a thru hike, an increase in the number of dogs they bring along is inevitable, along with the problems they cause. Thankfully, most don't make it all that far up the trail.
Section, weekend and day hiker dogs are a bigger problem. So far, (as a flip flopper) we've only encountered day hiker dogs on the weekends. But it's early in the season and not many are out on the northern sections of the trail now.