I had mine weighed at first, to make sure of the postage, and then bought a bunch of those stamps so I can mail from home. It's the stamp with the swallowtail butterfly on it... I forget the price. $1.10??? It works as long as you keep your letter (card) no thicker than 1/4". If it ends up thicker, you have to pay for the envelope as a "flat" (rather than letter) and the rate is somewhat higher.
edit: Ah! Sheri is right... it's a $.71 stamp, not $1.10.