What does this mean to you as a player? It means that programmers can create any number of applications using this data-- they can display your DR character's info almost anywhere at any time. And a skilled programmer could even track the info over time-- tell you how fast you leveled, how often you change your armor or gear, or how fast you've earned gold in the last day. And who knows what else people could come up with-- the best part about opening up information like this is that it gets used in all sorts of ways that no one could ever predict.
Jeff Freeman's exactly right: "This is really cool... just in case you don't get that." We're just scratching the surface of this stuff, but eventually you'll be able to do things like get text messages on your phone when your WoW auctions sell, or be able to monitor your guild's bank or your PvP team's wins via RSS (which itself can then plug into almost anything) When developers break out data like this for players, the possibilities are endless.