Browsing the deals on the forums and want to start taking advantage of some 2/1 3/1 deals.  However, I am worried that if I am looking at someones bookshelf that clicking order this book will actually order from the next available copy in the FIFO queue.  Is that how it works or does it really order from the person whom you are viewing their shelf?

If you click on Order This Book while looking at someone's shelf, you are requesting that particular person's copy of the book.  If you are just browsing books by titles or whatever, you will order FIFO.  Same thing applies with Posting a Book to someone's Wish List.

As long as you are really on that person's shelf, the order will go to that person.  Just make sure that you aren't looking at the larger book description when you order, because then it goes to the first person in the FIFO queue.