If you put the ISBN # in the search it'll bring up the book and tell you if it's WL and how many are wishing.  To find out how many are posted you can put the book on your reminder list.  THey are working on a way to put how many copies are posted and how often a book is requested on the listings. But right now you can only see how many copies are available on the reminder list.

Don't let the # discourage you from posting books.  I post a lot of heavily posted books and frequently they are requested form people using the Order More From Member button when I post a WL book. 

You can also load books into the TBR Pile under My Lists which is under My Account.  That'll tell you if a book is WL or not but now how many copies are posted into the system for non-WL books.

To find out how many books are in the system add the book to your reminder list.  Go to the description page and to the right click on the reminder button.  To see the reminder list click on My Account/List Tab/Reminder List

To see if there are members just wishing you can add to your TBR List - click on My Account/List/TBR/Add TBR and to find out how many are wishing on ce in your TBR click on the title.   It will give you a # of WL.  Or you can go to book browser, search WL books and a number will appear under the title.