Starting Monday, May14.2007 the postage rates for letter and parcels in the US will go up. The first class letter rate will be 41 cents.
However you may purchase the new "forever" stamp at the new rate of 41 cents and they will remain valid for sending letters regardless of any future rate increase. The stamps will not have a price printed on them.
But the price of 41 cents will not last forever! If the rate goes to 53 cents then that is what "forever" stamps will cost to purchase. Stamps purchased at a lower cost can still be used without having to add on the additional difference in postage.
Details of the new rates are available at www.usps.com