Dogs seem to be able to teach one another social behaviors pretty effectively. In formal training/artificial behaviors, it's less clear-cut to me.
I think Claudia Fugazza might
be doing some work based on social learning theories, although I am not familiar with her methods and not sure whether she is working on having the dog imitate the human, other dogs, or both. But if you're interested, she has a DVD set here: Welcome to Dogwise.com
Purely anecdotally, in my dogs, I have observed that Pongu can learn from watching Crookytail.
Here's a blog post about one instance I observed at the dog park a few days after Crookytail arrived from the shelter: Merciel's Dog Blog: A Quick Episode From The Dog Park
And here's another episode:
Background on that youtube: At the time, I was trying to get Crookytail to target the box lid with a paw touch as an early step in a trick that I was attempting to do with him. He had just
gotten proficient enough for me to attempt making a beginning-stage video clip of that step, so that was my original goal in filming him.
Pongu was not involved in that trick and I had never asked him to target the box lid; at that time Pongu and I were concentrating entirely on some Level 3 Rally exercises that he was having trouble with. So Pongu was never asked to do the paw-touch-to-box-lid movement, but he was
frequently asked to hold a Stay on the mat while it was Crooky's turn to work. Because Crooky is a slow learner who takes FOREVER to do anything, Pongu had seen Crooky trying (and failing) that exercise for several days.
Apparently that was sufficient for him to identify the correct movement, recognize when Crooky was screwing up, also
recognize when I was getting annoyed with Crooky by my tone of voice, and then step in and be a smug little butthead about shoving Crooky aside and offering the desired behavior in his place.
So clearly Pongu is capable of learning by observation. However, he is the only dog I've had who has been able to do this consistently (Crooky has shown a weak ability to learn via observation in fits and starts, but nothing reliable), and it's sort of useless to me in training, because he already learns faster than any other dog I've ever worked with. The quickest approach is always just to train Pongu directly.
train one dog in front of the other in order to get the observer to be more energetic when they switch turns -- Dog Mob will try to out-do each other and compete for my attention, so it's a good motivator -- but that's the only real use I've had for training one dog in front of the other.
These are just my observations, though. It's an interesting subject for sure.