I train service dogs, and the majority of the dogs I train are labs or GSDs (or mixes).
I definately agree with the above, that the differences in training are mostly personality differences, and you'll get a GSD who acts more like a lab, and vice-versa. It's like that with any breed. And the training that we do is basically the same for labs and GSDs, but of course we will make slight changes depending on the dogs' personality (use toys more for this dog, petting more for that one, work on some behaviors more than others if they need more practice, etc.).
But, from the dogs I've worked with, it seems that generally labs are much more people oriented. They are happy just to BE with you, and, although toy and treat motivated, will work well for praise and petting. They seem to spend a lot of time figuring out what YOU want.
GSDs, though, are always calculating how to get what THEY want. You have to be much more careful in introducing variable reinforcement, because if they don't think they're going to get their reward, they will quickly stop working. They also get creative in training - you ask them to do the same behavior they just did, and they'll find a new way to do it, particluarly if they thing that new way will get them the reward faster. They tend to be more interested in the environment, particularly things that move.
Of course, this is just what I've experienced, I haven't seen EVERY lab and GSD in the world, and I KNOW there are variations.