The Istanbul incident happened to myself and a friend a few years ago. We came out of a nice hotel and were walking to lunch. We were suddenly separated and he was surrounded by a circle of (apparently) fighting/arguing young men. Pushed his way out and didn't notice he'd been robbed until he reached in his pocket to pay for lunch!

Reported to the police (with help of conference organizers). Sadly we got the impression that they were more interested in how much exactly had been stolen (I'm afraid I got the idea it was so they would get their cut) rather than catching the people - in part b/c they seemed to know EXACTLY who the gang were and could quite easily have caught them since the area they worked was well known to the police