I don't have my GSD yet, but will be getting her this fall. I also have a 9 pound Papillon. I'll let you know how that goes.
But as far as big dogs/little dogs in general. My dog has no problem playing with big dogs. He loves other dogs and they play, if it gets too rough, he lets them know. I've yet to see a large dog that didn't seem to have a concept that Jester was smaller and they had to be more gentle. I would never leave him unsupervised with a dog that was substantially bigger, but when I'm around they seem to have a ton of fun.
But as far as big dogs/little dogs in general. My dog has no problem playing with big dogs. He loves other dogs and they play, if it gets too rough, he lets them know. I've yet to see a large dog that didn't seem to have a concept that Jester was smaller and they had to be more gentle. I would never leave him unsupervised with a dog that was substantially bigger, but when I'm around they seem to have a ton of fun.