I've noticed over and over a book will sit in the same spot in the wish list queue for months, then all of a sudden multiple copies are dumped into the system and my spot in the queue surges ahead. Sometimes it corresponds to holidays, but not always. Any theories why?

People sometimes have their account on hold during  summer vacation, Christmas, etc. so when they come back, having read all those books, they post them. :) 

Also, with best sellers, it comes a time when a lot of people own the books and they decide to get rid of them. That's why some books go from being wishlisted by hundreds of people to hundreds of copies in the system.

Also, each time PBS is featured in the media, we get a surge of new members posting books. 

Also I think those "copies posted" aren't necessarily different books.  (if someone in the know has different info please correct me) But I think if a book times out on wishers or gets cancelled by a wisher and then moved to the next wisher, it gets added to the count again.  It may happen with RC declines as well.  So if 1 copy is posted but the first 3 wishers time out and the 4th accepts, it might show up as 4 copies posted when you look at your WL stats when really it was just 1 book that affected 4 accounts. 

I think Mary is right - these surges reflect a single book moving through several wishers. Wishes are granted in the sense that these members have their chance at the book, but only one person actually receives it.

Until this was mentioned in the forums, I was extremely puzzled about how an obscure book could go without any activity for eighteen months, then suddenly have five copies posted in a week or two.

Another possibility, if it's a book that was published last year or the year before, is that multiple copies may be getting put on the remainder table at Borders or Barnes & Noble for a much lower price, so people who were waiting for a PBS copy to appear gave in and bought a cheaper-than-new copy, then posted it here.

All of those theories make sense, especially Mary's. Thanks, I've been wondering about that for a while.

I've also been noticing those 'surges'.  For example, I've been #2 on a wishlist for several months with no copies posted.  Then when I look again, it says 3 copies were posted last week...and I'm still number 2, or possibly 1.  Are these posting errors that members then cancel?  Copies posted to friends?  But I agree with the OP....nothing, nothing, nothing, then bam a bunch of copies.  If you're seeing movement in the wishlist, it's all good...about half the time, I don't think I advance on the wishlist in those circumstances.

Interesting theory Margaret, I hadn't thought of that one!

Works a bit in reverse too. I get maybe one request for a month. In the last 5 days, I have had 4 requests. Several books had been posted in 2009. :)