I remember when this used to be 1 lb.  I really don't understand the purpose of the new rules.   There are so many times I ended going to the post office when I could just have dropped a package into the mailbox.  Anyway has anyone attempted to place their mail in the box even though you know it's over 13 ounces?    Will the PO really mail it back to you?

The new rules came about with homeland security measures and the package will come back more often than not if you do not follow the rule I believe. There are a few carriers that take them, but sometimes those end getting sent back somewhere enroute anyway because someone down the line that is following the rules catches that the stamps have not been cancelled and sends it back.

You can use PBS postage, APC postage, or some other online postage on the over 13oz packages and be able to put them in a box, it is just packages over 13 ounces that have only stamps on them. If going to the post office is a hassle, the .43 postage fee might be worth it, especially when it comes with Instant Credit. I have two packages ready to mail right now that I used PBS postage because I want to drop them in a blue box.

It's a Homeland Security ruling Brundlefly.  Any package weighing more than 13 oz. must travel under 'trackable' postage or be passed over the counter to a USPS employee. 

Whether or not your package is returned, will depend on the type of postage used.  Any type of 'trackable' postage should be fine, if using stamps your package will most likely be returned.  And of course, all of the above will depend on the training of your local postal employees...but yes, they do return packages for this.

What if I use a label with DC on it, but use stamps as my postage?

Nope, its the purchaser of the postage (ie sender of the package) that has to be traceable, not the package itself. The DC is just a bar code to be scanned to confirm delivery so it can't track who sent the package. If the postage hasn't been paid for through an online account or credit card, it needs to be handed to a postal employee at retail counter if over 13oz.

I reallyl ike using the prepaid postage, for that very reason. I swing by the PO on my way to work and chuck the packages in. IF the package is too big, there is another mailbox i can go to that has the bigger opening-but I do have to get out of the car to use it...What I do for PBS!!

Yes, they will send it back to you, with a label on it explaining the problem.  The only time this happened to me the book was actually 10.5oz!  I know because I weigh them before I mail them.  I was so furious about having to go and wait in line, which is bad enough when I actually have a book that weighs over 13oz, but I wanted them to weigh the book and give me an apology, which they nicely did.  However, I use 2 or 3 different PO locations, so I now make a little mark on packages I send so if it is returned to me I know which location was the culprit.