if you don't have time to read the whole story, here is the moral: Don't just assume you have correct postage and put them in a mailbox - bring them into a post office and have a clerk double check them for you! It can save you a lot of heartache. Even better - give yourself enough time to weigh/check size of one sample completed invitation - and then place your order for stamps.
I took my invitations to the post office today, all beautifully calligraphied and stamped with specially ordered (i.e. overpriced) zazzle stamps. although i weighed a sample envelope at home on a food scale, i brought them in to the post office to double-check that they were really under the 1oz limit. They were - but my envelopes exceeded "letter size"!! Mind you, I did my research online to calculate postage before I ordered stamps, but my envelopes were square (which i did calculate extra postage for), but the USPS website did not mention a "max size" for square size. Apparently, there is. Heartbroken and embarrassed, I had to affix a second stamp to my invites.
I know at the end of the day this is such a minor thing and who cares about a little postage mess up, but it's still disappointing after all that hard work to make it perfect. So I thought I would share my story with fellow knotties in hopes that this mistake won't be repeated for any of you!