Today my cable lock with a 4 number combination just wouldn't open. It opened fine when I unlocked it from my top tube, but 5 minutes later it was seized. I finally gave up and had my wife bring the bolt cutters. I had her try her luck before cutting, as usually I've found that I'm doing something wrong and it hoped it would pop open. No luck, so at least that made me feel better.
I'd seen videos on how terrible cables are, but couldn't believe with 18" bolt cutters I cut the cable in one cut and it took all of 2 seconds. Cable is one of the midsized thickness ones, I'd guess 12mm. I even made sure I wasn't just lucky and when I got back home, but through the cable again no problem. The funny thing too is no one (~30 people) said one thing as I walked up to my bike to cut the cable. I guess bike thieves don't wear bright yellow or a bike helmet :-)
I was just running into the library to drop off some books, so I just used the cable lock. When I'm locking all day I use the U-lock on the rear wheel to lock it to the rack and use the cable on the front wheel.
Maybe now I'll just switch to a non quick release axel on the front wheel, since I now know first hand that cable locks are truly useless.
I guess I'm just frustrated I had to steal my own bike. At least it wasn't my U-lock, I've had problem with the key locking mechanism on those in the past too. I at least hope they are more difficult to cut.