I haven't looked into the details, but presumably there is some kind of DRM wrapped around the file download that Adobe's PDF readers recognize and use to block your reading it seven days after download or after first opening it.

Bernstein points out that many people buy books at full price and then after they are finished with them, re-sell at some small loss on Amazon anyway. Other people (like me, sadly) buy books, read them once, and then shelve them never to be opened again. For these sorts of people the limited license might be a good idea, at least from a cost perspective.

The problem (which people are pointing out in the comments on the blog entry) is that this model blocks use of the work for reference. A limited license might be useful for books that are more entertainment-oriented and less reference works, but it doesn't seem likely to catch on with weighty law tomes, even though those tomes tend to be pretty expensive.