Ive been stung a fair few times over the years.
First time was about 6 years ago. My CC bill arrived with a transaction of £180 to one2one. Which I called up, disputed and the sorted it.
Next time was another card, small amount, again noticed it when the bill came and disputed it.
The above two cards are never used online period.
The most recent was only a few weeks ago. The issuer called to ask if i was using the card in France and Italy.... which i wasnt, so again they sorted. (I actually figured this one out, this particular card is used for when I have a property project on for materials, so only gets used a few months of the year. Stupid i know, but i normally leave this card in my car and keep it for emergencies too. Now I usually get my car cleaned at one place all the time, so i figured someone there pinched it when i wasnt looking. I informed the cc company and the "manager" of the firm.
Two things to make you think though,
1) Once I had mislaid my switch card, so I called up the bank, and had it cancelled. A few months later after a good old fashioned spring clean I found it, somehow I mixed them up and used my old one in the atm, and guess what it worked! Called the bank up moaned and screamed and they made sure it was cancelled.
2) As Ive said I work in property. One of my places the tenants had left at the then of the tenancy. I then started to notice mail for a person I had no idea who it was. Opened the mail to find that a BT line in his name had been installed, and that this guy had registered on the electoral roll there too.
Calling BT, it turns out if there is a disconnected line, an engineer doesnt need to visit they can just reactivate it. Electoral roll, you just have to call and they put you one. BT cancelled the line after I proved I owned the place and that the last tenants didnt match up in name to this chappie. However the local council could not and would not remove his name from the roll, said I must wait until October when the new forms went out.
Think about it, the guys on the voters roll, and had a utility bill, all he needs next is proof of ID, ie passport, and he can rack up all kinda of CC's and loans. I even went as far as going down to the local police station, only to be told, there has been no crime so they can do jack.
Barclaycard have got to be the best card issuer I have come across. Its the only card I will use online becuase of their online fraud protection. Also they seem to actually call when something suspect is happening on your card. I was trying to buy a watch from dutyfree in Spain. The card failed the first time. As I was reaching into my wallet to get another, BC rang and asked if i was attempting to use my card, and how much for and to confirm if I was in Spain. They got it sorted there and then, and asked me to retry the card, and presto it all worked fine.