On a related note, I see there's now a site setup to help people lend/borrow books from other people using the feature on the Kindle and Nook readers. Ebook Fling describes itself as:
With 14-day lending now available on tens of thousands of Nook and Kindle books, eBook Fling makes it possible for readers across America to borrow and share their ebooks. Lend an ebook, earn a credit, and borrow any other for free! It's 100% safe with the book returned in 14 days guaranteed.
Having been contemplating an ebook reader myself I'm still trying to wrap my head around buying books as presents for someone. We tend to give each other books quite a lot as presents in our family and not having a physical medium to wrap, or giving someone an envelope or gift card just isn't the same. Physical stores need something too, so you can still buy a book at the supermarket or you favourite book store, we need some sort of cheap, disposable memory card, or something like the Playbutton, or maybe just small CDs, the person then has a backup as well.