The climate cycles on mars are going to be an interesting thing for geologists to study, as mars is in some ways very like earth, but has huge variations in its axial tilt.

Universe today has an article on more (probably debatable) evidence of groundwater on mars: http://www.universetoday.com/2008/12/11/groundwater-may-have-played-important-role-in-shaping-mars/

I don't have any objection to groundwater on mars: on a planet with extensive ice deposits, volcanoes and meteorite craters it would be surprising if it didn't occur occasionally. However this article seems to be claiming a fairly recent timing for it, which Nick will probably have something to say about, unless he's got bored of debunking stories like these...