Tim Bray makes some excellent points about book sharing and electronic readers:
Those in the business of books are unlikely to be losing sleep because I’m whining about sharing, but they’d better be careful. We saw what happened in the music space, and I think authors are way more vulnerable than musicians. First off, no matter how much piracy is going on, a musician can always fall back on live performance. Second, your average novel, compared to music or video, is remarkably small; trivially easy to share once the digital locks are broken, as broken they will be.
The thing about authors and musicans is key - authors really don't have anything else to fall back on. Too much greed on the part of publishers could create real problems. Right now there's limited sharing; with the Kindle app, you can share across 5 devices - so I can share one account with my wife.
However, I can't feasibly pass a book to my mom or sister (I've done this with physical books). The issues of space (they live in other states) and credit card sharing get in the way. THis is going to end up being a problem, and if the publishers don't create a reasonable response, the response that arises will be one they won't like.