It depends on the device. For mobile phones, the DRM is usually harder to break than on a PC. The reason is you have much less control over your mobile phone than you do your PC. For standard's based DRM, OMA DRM 1.0 is the most widely available. Within OMA DRM 1.0, you have three categories, forward-locking, combined delivery and separate delivery. Forward locking just prevents you from forwarding the content to another device. Combined delivery and separate delivery both rely on rights which govern how you can use the content you paid for (number of uses, use between certain dates, etc). Separate delivery also entails encryption of the content with the key being delivered, along with the rights, separately from the content.
There is also OMA DRM 2.0 which is currently not available for mobile devices yet (except the Nokia n91). Both Microsoft's and Apple's DRM technologies are proprietary and rely on end-user device clients.
All in all, DRM is getting better in that it makes it harder for pirates to steal music without infringing on the rights of the legitimate purchasers of the music. DRM has a bad rap because of that. Right now DRM is very constricting and pisses people off because they can't use the content they paid for on their devices. But that's the price we have to pay because of pirates. OMA DRM 2.0 solves some of this but as was alluded to earlier, unless you completely eliminate the "analog hole" you'll never be able to stop piracy.