I've heard from a police officer friend that fake credit cards have become a BIG problem. Some of the criminals doing this type of identity theft have mobile credit card-making machines, operating in cars or other locations right around the corner from where thieves are stealing people's wallets.
The thieves bring the wallets with real credit cards to the card maker, who makes fake IDs and fake credit cards on the spot. They create an ID with a photo of a member of their theft ring and a fake name, and a fake credit card using a number from a real stolen credit card and the same fake name that's on the fake ID. The person who's on the ID then goes to a nearby store to buy merchandise (often for later sale) with the credit card before the victim reports their cards as stolen, and it may be expensive stuff.
You may want to program the phone numbers for your credit card companies into your cell phone and perhaps keep them on a card tucked in your pocket, too, so that you can call IMMEDIATELY if your cards are lost or stolen. Even better - carry your wallet in a secure spot where thieves can't reach it. If you need to declutter your wallet to thin it down in order to fit it into an inside pocket, that's a small price to pay for avoiding theft and all the hassles that come with it.
If you are a merchant who accepts credit cards, look carefully at the back of each credit card. On the fake cards, the signature strip does not look like the strip you'd find on a legit card. Apparently they haven't gotten that part right on the mobile credit card-making machines yet.
My police officer friend responds to many calls involving pickpockets, identity theft, retail fraud and shoplifting. He arrested someone for a fraudulent transaction last night, and the credit card from which the numbers were lifted had been stolen less than one half hour before that fraudulent transaction. Given the current state of the economy, this is a HUGE problem right now. It costs you, your credit card issuer and the merchants whose goods are stolen.
It's much easier for police to catch the thieves if you report lost cards right away - as soon as you can possibly make a call after you realize they're gone. If the card is reported stolen before any fraudulent transactions, it goes into the system right away, and the cashier gets an alert when trying to process the sale. They can get store security and police, and the thief is usually caught. For most incidents, this is a felony charge, likely to result in jail time for convicted offenders.
I was robbed a few years ago and was able to cancel my cards right away. There were no fraudulent transactions, so I only had to deal with the annoying process of replacing my cards - much easier than the consequences of paying for purchases I didn't make or having a damaged credit rating.