From the FAQ: Can I lend books from my Nook?
"Yes. With our new LendMe™ technology, you can now share from nook to nook. But it doesn’t stop there. Starting Nov. 30th, you can lend to and from any device with the Barnes & Noble eReader app, including PC, Mac OS®, BlackBerry®, iPhone™ and iPod® touch. All you need to know is your friend’s email address. You can lend many of your eBooks one time for a maximum of 14 days. When you use our LendMe™ technology, you will not be able to read your eBook while it is on loan, but you always get it back."
I think this is a typo - I think they meant one at a time - not one time. As you will see, later in the answer it says, "you always get it back".
At any rate, whichever is the correct answer, as good as this idea is, I don't see it taking off, because the publishers are all going to throw fits and deny B&N from offering LendMe on their titles.
Daithi, if they get back to you with a different answer, please let me know