The bad news is you can only lend a book out one time for fourteen days. While the book is "lent" you can't read it. Amazon CEO calls this feature a joke but B&N claims 80% of book authors will allow lending. It's a nice feature to have and opens up the door to electronic lending - a great thing.

To lend a book on your nookColor you first need to know if it is a "Lend-Me" item. You can do this looking at the book cover, lendable items have a "Lend-Me" ribbon at the top. To lend this item tap and hold your finger on the book cover until you get a pop-up.  Select "Lend-Me". From here you can find contacts you've added to your nook or view your Facebook contents.  Select a person and include a message.  They will have 7 days to accept the lending and after they do the book will be theirs for 14 days.