I found this email regarding MRO's findings (9/07):
[Another new finding from that camera may help undermine arguments that very ancient Mars had a wet climate on a sustained basis. Landscapes with branched channels and fan-like deposits typical of liquid flows were found around several impact craters. Images show close association between some of those flow features and ponded deposits interpreted as material melted by the impact of a meteoroid into ice-rich crust. This new evidence supports a hypothesis that ancient water flows on the surface were episodic, linked to impact events and subsurface heating, and not necessarily the result of precipitation in a sustained warmer climate. Crater-digging impacts were larger and more numerous during the early Martian era when large drainage networks and other signs of surface water were carved on many parts of the planet. ]
http://www.nasa.gov/mission_pages/MRO/news/mro-20070920.html