[joe42]

The textbook renting service Kindle introduced last month depends quite heavily on DRM.

I verified recently that I can "rent" a book for, say, 30% of its "buy" price, remove the DRM, and be left with a DRM-free book (not limited to a month rental).

[mahyarm]

It's padlock DRM, cheap, easy and keeps out the vast majority of casual piraters by being more of a hassle than just paying the usual $10. Biggest bang for the buck. People who are really cheap or poor would just go to the library and get it for free in some form or torrent it anyway and you wont get any money from those people.