My best friend is an operations manager for the local power company. He told me that thieves are even starting to steal aluminum cable, in fact he mentioned that someone used a backhoe to pull about 1,000 feet of 4/0 triplex out of conduit at a construction site. It's not just copper anymore.
I read an article in the newspaper recently about the extremes that recyclers are having to go through to curb metal theft. They require a photo ID, they take a photo of the seller and they copy the license plate number of their vehicle. One thief came into a recycler with seven brand-new 2,500' reels of #10 copper THHN. In an effort to stall him, the told him that they couldn't take it on the reels, so they asked him to take it outside and remove it from them. This gave them enough time to contact the police who arrived and promptly arrested the guy and his accomplice. It turns out that the wire was stolen from a job site where my son is working.