Just because there's water doesn't mean the moon is habitable. It's still a barren wasteland lacking an atmosphere. The importance of this discovery is that it opens up a route to get to Mars.
Water would allow for bases to be established on the moon. (Think something along the lines of research stations in Antarctica; there's a helluva lot of water there, but it's hardly a hospitable or desirable environment.) The water could be used both for consumption in the base and for splitting into hydrogen fuel for rockets. And since fuel for return trips from the moon could be manufactured on the moon, less would have to be sent up from Earth, making it a lighter (and therefore cheaper) takeoff.
This also makes it viable to do simulations for what a stay on Mars may be like. One idea I've heard on how to prepare astronauts for Mars is to establish a research base similar to what would be built on Mars on the far side of the moon. When astronauts have travelled to the moon in the past, they were always on the near side, giving them a view of Earth and reminding them that they're (on a cosmic scale) close to home. On Mars, though, Earth would be nothing more than a rather bright star in the sky, and some theorize that this could weigh quite heavily on the minds of those on Mars. A far-side-of-the-moon base would simulate that effect. And now that water has been found on the moon, that would make the upkeep of such a base that much more viable.
Then again, some people simply don't see a point to space travel and exploration.
