Jumping up at visitors

I know a couple of dogs that jump up at anyone coming over to visit. They do this to greet the people and just want to get petted by them. Now with a small dog I don't think its too big of a problem, but what if a German Shepherd does this?
I personaly don't mind a dog jumping up at me, but I'm sure a lot of people do mind. The owners say they don't know how to make the dog stop doing this, maybe someone here has some good tips.
With my own dogs I never had this problem at all, so I'm not sure what would make the dog start behaving like this in the first place...
Anyone want to share some thoughts on this subject?

Paula

I have a GSD. He doesn't jump on people because he listens to me. We have band practice at my house every week so there is a group of people coming in. He'll greet them and then move on (part of the GSD personality). If he gets too excited and tries to jump, I put him in a down/stay to calm him down. When I get home, and he gets really excited, I pretty much ignore him until I'm settled in- put my keys away, put my computer bag in the office, go change my clothes. Then I'll pay attention to him. By then he's calmed down, following me around while I do my stuff.

I have this problem with my dog, who is a lab X, when she jumps we turn around saying OFF, followed by Sit, only then does she get some attention. If I am home and my husband returns from work, I make her sit and wait before he comes in, when he comes through the door, if she remains sitting she gets attention, otherwise he ignore's her until she sits. We are getting there, its slow work she just gets so excited when people come by to visit. if we have visitors to the home we put her on her leash before opening the door and make her sit.