The problem with any DRM is that it exists to protect the company that implements it at the expense of the customer's short and long term interests. It's never a good business plan to put your own company's interest ahead of your customer's. Well at least you don't want them to know about it.
The only way DRM can be successful is if the customer doesn't know it exists. I've worked with many software companies that have tried to implement software copy protection by requiring hardware dongles or adapters to be installed in the computer. It's not a pleasant experience to have to explain to a company that their server was down for a couple of days because although they paid thousands of dollars for the software the vendors DRM dongle broke. All the companies I know that have tried this have reversed the decision or gone out of business.
The best example of DRM that I can think of that actually works is the stamp of "Property of Littleville Public Library" stamped in books. You don't notice it unless you forgot to return it and if you have that sitting in your library you must feel like you're two inches high (if you have any self respect).
People don't remove the copyright information from the e-books I don't know why we can't just have a simple scheme of stamping the Owner, Purchaser, Company purchased from and a transaction number to the book and have a legal statement that you can't remove this information. Something like the "If you bought this book without a cover you're breaking the law". If a company did this they'd get my business.
Can it be enforced? No but neither can any DRM.