Ah, that's a great one!
Yesterday morning, when LynneK and I were riding on the lakefront path, we passed a couple of folks with dogs. I commented that I wished they'd walk their dogs on the outside of the path, though that's seldom the case. Lynne said, "They have a lot more faith in their dogs than I do!" I love dogs, but even playfulness could be disasterous on a bike.
The yesterday afternoon I took the bike out to try out a saddle, rode through a park where dogs are sometimes off leash. Two little guys frisked up to me, one stood right in front of me in the path where I'd come to a complete stop. Friendly, but a solid little bundle, and I wouldn't have wanted to connect with a wheel!
As you say, a well-trained guide dog is a joy to be around.