I requested a book last month and it has gone lost in the mail (PBS canceled it today). Should I email the sender for any reason? I mean... is there some etiquette I should follow? 

What I've done in the past is PM the sender to let them know that I'm still hopeful that the book will show up, and that if it does I'll be sure and mark it received in my Transaction Archive.  If it was a wishlist book, the system automatically put you back at the top of the wishlist.  You might want to put the wish for that book on hold for a couple of weeks to make sure you don't get two copies in the mail.

In the Help Center, there is a page called A book I requested is lost in the mail. What now?  From that page -

If a book you requested does not arrive by the 26th day (the 35th day if the sender or requestor is outside the contiguous US) after it was marked mailed, it will be declared lost in the mail at PBS. The requestor does not mark the book Lost; the system does this. 

The requestor will get credit back, and the book will go onto the Wish List (if there are no available copies in the system) or the Reminder List (if there are other copies available to request).  If the book was a Wish List book when it was requested before, the requestor will go back to his or her previous place "in line" for the book.

• However, this does not mean that the book is definitely lost.  Sometimes it is merely delayed en route.
• If the book arrives after it has been declared Lost, the requestor must mark it received from the Transaction Archive.
  • At this time, the credit will be taken back and given to the sender for sending the book.

What you should do if a book you requested is declared Lost in the Mail:

• Contact the sender, to find out if mailing was delayed for some reason.
  • you can do this from your Transaction Archive, using the PM button on this Lost transaction in that list.

• If the mailing was not delayed, the sender should call 800-ASK-USPS or go to http://postalinspectors.uspis.gov/forms/MLNtRcvd.aspx (the Postal Inspection Service's website) and input the information online there . This will help USPS try to recover the book if it truly has been lost in the mail.
• Don't re-request the book for at least 2 weeks, unless you are willing to run the risk of getting two copies (and paying a credit for both).

If you are having a lot of books declared "Lost" en route to you:

• You should investigate this.  Excessive unreceived books may jeopardize your membership.
  • Numerous books sent separately but not arriving at your address implies that something is wrong with your mail delivery.
  • Requestors are responsible for providing correct, dependable mailing information to senders.
• Check your address in your Account Settings, to be sure that it is correct.
• You can send a PM to the sender of any or all of the lost books, to ask if the book was mailed late, by any chance, as described above.
• Talk to your PO and mail carrier to see if the book might have been misdelivered to a neighbor.
• Consider using a PO box or alternate (ie, work) address until the matter is sorted out.

What Laura said & Jenna posted   

Check the state the book is arriving from; Alaska, Hawaii, Puerto Rico and APO addresses can take a bit longer (seem to average 5 weeks).

Otherwise, some of these books never arrive, some arrive late, and some arrive a year later with postage dated on the 'mailed' date...go figure.  But PBS recommends waiting to reorder JIC.

It's being mailed from IL to CA, so nothing strange there. It wasn't a WL book and there is currently another copy in the system. So I'll just give it a few weeks and reorder.

Goodness! My book finally got here -- 9 days after being declared lost in the mail. The postage on the wrapper was bought on the same day the book was canceled in the system (I also emailed her that day). So the sender must've realized that she never mailed the book, and did so after it went lost.

It would have been nice of her to at least email me about it. I received no communication whatsoever. I would have liked to know that she WAS mailing it after-the-fact so that i'd know not to order another copy. Geeze.

On top of all this, the book has a somewhat large water stain on the back cover. Grrrrrr. I don't intend to re-swap it, so I didn't mark it RWAP. I've already had enough problem swaps in the past year that I can't stomach dealing with another one.

There is a special category to mark late mailing dates.  They are REQUIRED to let you know if they are going to mail more than four days late.

Frankly, it is important that we do mark RWAP.  I'll often will not ask for a credit.  But the only way they will know they cannot get away with such behavior is if we mark it.  This way PBS can also tell if it is a one time problem or an ongoing issue. 

Yes, late mailing requires notification and even permission (after 7 to 10 days IIRC).  Do RWAP those, especially when they arrive with counter postage (excellent proof of late mailing).  You won't have to fight over a credit return, but do note it in the system for TPTB...if they notice a pattern the other member could have their account reviewed.

Although you can mark a book "Received with a Problem - Late Postmark" ... please note that it is not marked as an actual RWAP in the transaction archive like other RWAPs are. The late postmark gets noted and if the sender mails a lot of books late, then their account might get reviewed.

You should not ask for your credit back on a late postmark.

I agree that it's a good idea to mark a water damaged book Received with a Problem (RWAP) even if you don't intend to ask for your credit back.  Consider it a favor to the next member who orders a book from that sender, who may now double check to be sure the book is actually postable before mailing.

When we check the RWAP box, and choose "damaged by sender", the default is to ask for our credit back, but we can uncheck that choice.

I had this same problem with two books in a row going lost (and I started a threat in the CMT section called "Honest, the book has not arrived!" where we discussed it too.)

As it says, I would contact the person, because they too need assurance that the receiver isn't on a long vacation or forgot to mark it--although PBS seems to assume the receiver is delinquet with its e-mails and activity listing of "One Book To Mark Received."

I've gotten a handful of books since the two went lost, and the first person whose book went lost e-mailed me to say they did mail it on time, so I think it's legitimately lost (unless the mail carrier just isn't bringing it yet). 

But getting one with a postmark after it was marked lost is a problem. I'm holding off on ordering a new copy of the two of mine I didn't get, but if I receive one with a postmark after the book was declared lost, I will not be happy. That's inconsiderate and selfish.