The Phoenix has a scoop-full of dirt and who knows what else ready to go into the oven. Hope they discover everything they think may be there, especially water. Salt may be involved in the dig too. Salt should be a common mineral found widely across the Universe. The trick is finding it in high concentrations like in dried up lake/ocean beds. That kind of find would argue strongly for liquid water in the surface at some time in the near to very distant past. It also might be an indicator of life not dissimilar to life in our oceans.
It would be neat to find gases cooking out of the dirt that only could come from life processes. Asking for to much maybe not, dreamers are good at dreaming. I'm one of the dreamers.
While all this robot exploration is good, if we had people on the surface they might find something overlooked by a machine. They would have considerable higher degree of independent action and ability to take advantage of serendipity. Imagine that the scoop on the Phoenix makes a few scrapes on the ground, uncovers a large rock and can scoop no more. Now imagine the human doing the same thing. What is the most likely action of the human. Scratch the rock loose to see what's under it. Maybe a fossil. Machine wouldn't know squat about that, but a human would. We need humans involved as quickly as possible in exploration anywhere we go. Machines are fine for first dig, so to speak, but humans have the brains and discretion to "go with the flow."