Someone told me about Paypal Ship Now years ago. I just sort of assumed everyone knew about it... but it really does seem to be a "secret" link in Paypal. Well... not so secret now. You DO have to be logged in for the link to work.
It's a good thing to know about as we don't ALWAYS receive a Paypal payment for something. I take credit cards via my website. Old friends send me checks. I still get money orders from time to time. But you can still ship 1st class USPS WITH tracking using that link. The shipping window is almost identical to Paypal's regular shipping window...only the address is black. Fill it in and the rest is exactly the same.
Paypal Ship Now is a very good thing... spread the word!