I have had a book on my list for ever. It finally was my turn and the postage was accepted and printed. now the transaction is cancelled and I am #2 on the wish list? What happened? 

Its very possible that you were offered the book in the #2 position. Sometimes the front of the lines get clogged up with people with the book on Hold and the offers are going to people other than #1. I've seen as far down as #7 and #8 being offered books. I think I have about 6 or 7 books on my Wish List where I am #1, but have it on hold so the offers are repeatedly going to #2.

What types of books are the most popular to post on this site?  Mystery?  Romance? 

Brenda, 

You can see a list of the top requested and wished for books at this link: http://www.paperbackswap.com/book/top_50.php#t=requested

just wanted to update.. it looks like the book was just not marked as sent. I got it today! A great surprise after a long and icky morning!!