This BBCnews science report summarizes the most recent findings from Mars researches. In a nutshell: there's quite a bit of water on Mars, enough to cover the entire planet in a very shallow ocean if it were all released at once. This is very promising for, say, future human exploration. Not only can you use the water for drinking, but also creating rocket fuel for your return trip, making the craft that needs to get you there far lighter (and hence less expensive).