This was interesting, since I colleague (lady ~40ish very local) commented after me putting a hand on her shoulder. We are a small office and had been small-talking for a year or so (so we know each other fairly well), when she made a good joke I put my hand on her shoulder and tapped it a bit, without really thinking about it..
Afterward she explained that her husband would not like that other men were touching her in the office and something about that it's a good thing that he's not here, to make me feel she didn't really mind. No big deal but I think nobody from my home culture would have made such a comment for such a innocent shoulder tap.
Interested to hear some more experiences. I'm also fascinated by that the locals never hug each other, but they seems very happy to walk arm in arm on the streets.