A number of manufacturer's websites have led me to this site – Wilhelm Imaging Research. This is an absolutely invaluable resource if you are in the least bit interested in how long and under what conditions your prints will last. There is a link to a free read 'The Permanence and Care of Color Photographs', that, although it dates from 1992, is a great introduction to the issues at hand (and a reminder that fading and permanence issues are not new to the digital age as shown by the catastrophic performance of Kodacolor film and prints introduced in the 1940s)). Other links provide current test results for a variety of printers, inks and papers.
The longevity test strategy developed by Wilhelm Imaging Research is becoming the de-facto standard for all the major manufacturers. It's well worth checking out this resource when making decisions as to what printer, ink or paper to buy.