I've had three attempts. None successful. I've been to most of the cities mentioned here, except Barcelona. I do try to be very careful when traveling, and split up cash/credit cards, as well as having a hidden interior pocket in my shirts.

Gypsy kid in Bucharest, Romania. Caught him with my hand in my pocket. He was scared until he realized that I wasn't going to smack him, and only yell.

Team of three on a Buenos Aires subway. One blocked getting on the train, one went for my pants pockets, the other for my shirt pocket. Caught the last one. Grabbed her fingers, and bent them back a bit. Yelled "Thief" in spanish. She smacked me with a half filled plastic bottle of pop. Then all three vanished off the train, as the doors were closing.

Last, was snuck up on in Quito in the evening, walking along a street. Saw a couple of very shady characters on the corner, and started to turn around, just as a guy was trying to put his hand into my pants pocket.