I still have books on my shelf that I posted in 2007.  I think it depends on how much space people have as to whether or not they need to get rid of them quickly.

I usually keep a book on my shelf for a year, unless it's the only one in the system, and then I'll keep it on there longer.  Pat

It depends.  I really don't have much room to hold many books so I put them on here while I have the room to hold them, but when I want to clear out some space, I will sometimes sift through the books I have & take some off of here & donate them or give them away.

If you're wanting to get rid of some books that have been on your shelf awhile, I would suggest offering a deal on them.  For instance, if you run a "2 for 1" deal, then if someone orders 1 book from you, they would also get another book off of your shelf as a freebie.  They would get 2 books for just 1 credit.  People run deals a lot over on the Book Bazaar.

I have some that have been on for three years.  I just got a FIFO order earlier this week for such a book. They don't come very often, but a credit's a credit, eh?  I have a couple boxes in my home office--storage is not a problem.

I will offer deals or give books away once or twice a year.  Usually right before I add books.  Right now all of my shelf fits into one box, so I'm quite content to ignore it.  

I have books on my shelf that I posted right after I joined three years ago.  I figure that they've spent all this time working their way up the FIFO line, and it would be a shame to remove them when they might be next up for request.  In fact, in the last few months I've gotten some requests for books I posted three years ago.

I just leave em there....never know when someone might see one they want and order it.

-RD

It's really up to you.  Are they stressing you out?  If you don't need credits and the book clutter is stressing you out then purge them.  Especially if they are heavily posted.  You won't be harming PBS if you remove your Nora Roberts, Dan Browns, Grishams etc.,, (just naming some heavily posted authors off the top of my head).  If you need credits and are tired of looking at the books run a deal and get them out.

If the book clutter isn't bothering you and you have the space then leave them and see what happens.

Since I had to majorly downsize my living space, I donate anything that hasn't been ordered when I'm ready to make a thrift store run.  Now I don't even really post the more heavily posted stuff. I read it and purge it.  I only order WL books at this point and always seem to have a large credit stash.  I have WL books I can read and post if I get short on credits.  So I am quick to purge rather than let them sit on my shelf for months or years.

Depends. I make a trip once a month to my local UBS. I decide then what goes and what stays.

I have storage room for about 200 books for my PBS bookshelf (in guest room closet) so as long as there is space there I won't get rid of books since I figure the popular MMPBs are slowly moving up the FIFO line.  I offer deals on my children's book series and give away quite a few so I haven't had issues yet with having to whittle down my bookshelf.

I don't bother to list anything that's not wishlisted or the only copy in the system. That's just my preference because I don't have a lot of extra space. I donate everything else to my local Friends of the Library.

Once I've put a book on my bookshelf I leave it there.  I have one box for my PBS books.  I'm more picky about what I post now, though.  If there are a bunch of copies in the system, I give it away.  I also give away books that are postable but someone may not like.  I tend to only post hardcovers if they're wishlisted or the only copy in the system.

I figure the books I've already posted are working their way through FIFO and I'm better off leaving those books in line while avoiding posting to long lines.

I keep most books for some time.  About every other year, we make a trip to BookThing of Baltimore, and I pull books I don't think will be requested, along with unpostables, and donate them there.  

If I had closer access to BookThing, I'd probably do the same.  I love BookThing!

I'm just terrible.  I have a friend building me bookshelves for my son's ex-room.  Maybe I'll start calling it "thuh LIGH-brury."

I have books posted from when I joined a year and a half ago.  I only have a handful of books posted right now.   I just had a book from my first day posting requested last week.  Since they have been moving up the FIFO and I only have a few, I'll keep them for a while longer.

As many have said, it depends.  IMHO it's hardly worth posting anything that already has more than a dozen copies in the system.  As for everything else, if it's been sitting there for a year and is the sort of thing the library booksale might want, it goes there right before the sale.  If it's science fiction and I'm going to a convention (in the car), it goes there to the freebie table.  (I have yet to see any SF books left on the freebie table by the end of the convention.)  Anything I have that doesn't meet the (in my opinion, somewhat oddly strict[*] posting rules) goes to those places as well.

[*] I find the idea that a tiny water spot makes a book unpostable, but a missing dust jacket on a hardcover does not, to be peculiar, but maybe that's just me.

Aside from some old college textbooks, everything's stayed on my shelf since I joined.  When I move, I'll probably donate whatever books I have left in the trade box, but for now they aren't taking up too much room, so I keep them there.