One of the primary reasons that Gale crater was chosen as the landing spot for the Curiosity rover was that it contains rich sedimentary deposits; old dried-up channels can be seen cutting through the crater rim, where the once-flowing water left behind alluvial fan deposits of gravel on the crater floor.
The channels and deposits could be easily seen in orbital photographs taken of the area. It was hoped that Curiosity would be able to confirm this from in-situ examination of the terrain here, and it has done just that.
Not only was there water here, but it was a fast-moving stream up to about hip-deep according to the new studies done by the rover, and reported yesterday in a NASA press briefing.
See Examiner.com for the full article and slideshow.