I've always wanted to do more with my ebooks; g.e to make a gift of those I'm no longer interested in, or to swap an ebook with a friend.
As for lending :the postive aspect of it is that one can read these Kindle-ebooks on a lot of devices. The book is protected, but the system also has a kind of flexibility through the apps.
And it could give a boost to ereading, as PC-users/iPhoners could try ereading without having to buy an ereader.
Perhaps Amazon could start its own online-library as well.

I'm intrigued how it all will work out.