How long do I keep books on my swap list? Most of them I have had on there since I joined.

Carolyn,  some books will take a while to be ordered, others, depending on demand will move more quickly.  It's your preference how long you want to keep books on your shelf.  I personally will wait as long as it takes (some heavily posted books will take years to be ordered, if at all). You can add books from  your shelf to your reminder list, that will show how many copies are in the system, not where you are in the FIFO (first in/first out), and based on this some people won't even post a book with too many copies available. Or they'll cull their shelves periodically based on how many books they have incoming and/or shelf space.  You can also go the book bazaar forum and offer deals to move your shelf more quickly.  There are many threads with creative ways to enhance your swapping experience.

You keep them until they are requested or you decide you are tired of looking at them. It's your choice.

I revamp my bookshelf every year. I double check each of my books (making sure my virtual shelf and my physical one are the same. Looking thru my TBR lists and sometimes deleting books that  aren't so rare. I also trade books with family and co-workers. It is you shelf to add or delete anytime you want. Lately I have had requests for books that have been there for 2 years. You just never know.

I've got some books that I put on my bookshelf right after I joined in October 2009.  Since I have plenty of space, I figure I'll leave them there until someone requests them.  I've actually had some recent requests for some of these books, so I know that they do move up in the system, albeit sometimes rather slowly.  I don't want to delete any of my books that have been on my shelf for a long time, because I figure they've already spent two or three years moving up the FIFO line--it'd be a shame if I delete a book right before getting a request for that book!

When you post a book here, you get in line for sending it.  So the longer it has been on your shelf, the higher up you should be in the sending line.  I keep mine on my bookshelf forever.  Some members cull regularly.

I have plenty of storage space so keep mine for 2-3 years generally.  If a charity requests a bunch of a certain genre, I will cull and give them away that way.  but I have posted books by very popular authors such as Dan Brown and gotten them requested pretty quickly despite some of them showing hundreds already posted.