does anyone know the USPS site where I can print the 13 oz rule where I can mail over 13 oz. with PBS Postage. My post office is questioning this.  Thanks.

Here's a page from 2007 where it is discussed.  I'm looking for something more recent or "official-looking" for you.

http://www.usps.com/mailpro/2007/septoct/page4.html

Edit:

Here's what a bit more searching came up with. 

1) July 2007 press release explaining the 13 ounce rule

http://www.usps.com/communications/newsroom/2007/pr07_058.htm

2) Here's a little bit talking about the security reasons for the rule

http://www.usps.com/aviationsecurity/

Also, searching the FAQs for "13 ounce rule" will give some links about it that you might find useful.

Try this link...http://faq.usps.com/eCustomer/iq/usps/request.do?session={c58c4660-9669-11dd-6a07-000000000000}&event=5&view()=c%7B07797ce0-57e2-11dc-51b6-000000000000%7D&objectId=&eksObjectId=&objectType=Case&isJumpEnabled=false&isContentJumpEnabled=false&vendorKey=&objTitle=&versionId=1223&searchProperties=type:natural&naturalAdvance=false&allStr=&phraseStr=&anyStr=&noneStr=&keywordStr=&tTitle=&topicFromSub=&topicsORSubUrl=&report(0000)=p{8e8226c0-6974-11dd-e6c4-000000000000}&bcobjectId={e4ae5a10-6973-11dd-e6c4-000000000000}&search=&topicAndSubtopic=About%20USPS$ALL

I just mailed 2 books that were over the 13oz.  I thought media mail was except but reading hear looks like that is incorrect.   What happens since I did not hand it to a clerk but put it in the blue box? 

Ginny, if the packages held only postal stamps, they will probably be returned to you at home. If they do come back to you, please PM the people waiting so they know what the delay is.

What I do is keep some APC "stamps" on hand. They are an exception to the rule and are treated just like online postage so you don't haveto hand them to the clerk. That way when the lines are long or I get there after the counters are closed, I can just toss them in the mail slot or the blue box out from.

The 13oz rule only applies if you have actual STAMPS on your package, your ok if you print your postage online.