While most scientists seem to be finding more and more evidence of a "wet" Mars, some are making strong arguments for quite the opposite:

One study reveals that a region rich in the mineral olivine - which suggests it is has been "dry" for about 3 billion years - is actually four times larger than previously thought. That adds to a growing body of evidence suggesting Mars was mostly cold and dry - and not warm and wet - in the past.

The second study asserts that subsurface reactions of olivine and water could produce enough methane to account for recent observations of the gas in the atmosphere, removing the need to invoke living microbes to do the job.

Of course, this gives us even better reasons to send more probes, so I think it all ends up being good.