For a long time, it was purse snatchers, then expensive athletic shoes. Smartphone thefts are now on the rise. There's apparently a lucrative "Black Market" for stolen phones.
The FCC says 30-40% of all robberies in large cities involve a smartphone. They Recommend password protecting your phone before it gets into the wrong hands.
CNN anchor Carol Costello had her phone ripped from her hand while having a conversation as she walked down an Atlanta street in the middle of the day.

"Three teenagers ran up behind me. One of them grabbed my iPhone. Stupidly, I struggled to hold onto it. But he was a big guy, and he pulled out a chunk of my hair. I let go,”

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- Carol Costello, CNN

Law enforcement officials in several major cities are calling for the  manufacturers to develop a "kill switch" that will make smartphone useless if stolen. I don't think they'll be in a hurry to do that. If your phone is stolen, and you have an existing contract, you'll have to pay full price for a new one.
IT departments of many large corporations already have their own wipe and mobile device management policies. It's becoming increasingly widespread.
I have an iphone 4S, and I've downloaded the "Find my iphone" app. I guess that's a start.