Or do you get the first-in copy of that book which may belong to another member?

If you are looking at another member's bookshelf and click "Order this book," you will get the book from that member.

If you order from the book description page you will get the first copy to be posted.  So if you want it from a specific person you need to be on their shelf.

Thanks everyone - that's what I was hoping, that that particlar member would get the transaction. I've never ordered directly from a Bookshelf before so I wanted to make sure.

Beware, even if you are currently looking at someone's shelf.. and see a book you might like.. and click the description..... if you click Order from the Description page it will NOT go to that person, but rather to the first person who posted the book.  So.. if you DO go to descriiption to read a little more about a book, make sure you go back to their shelf before you actually click order.

Something to consider too.  I had someone order a book from me by the Book Description.  I sent the book she asked for and got hit with a RWAP!  Why?  The book had been read once, no damage, why, why?  Because the book description was for a different book!  So, if you've found something you think you'll like from the book description I'd check Amazon.com for the book title to be sure they matched.