Not even off of its lander yet, and Spirit has already found evidence of fossil life on Mars.

The upside: no more worries about biological contamination of Mars by manned missions!

The downside: someone is bound to make the argument, as against a return to the Moon, that we've "been there, done that" (never mind it was Homo Habilis or some such anthropoid and not, strictly speaking, "we" who did it).

[via Sven Knuth. And yes, I'm joking here.]