That methane has been detected in the Martian atmosphere seems to be irrefutable. The next puzzle is to determine its source: although Terrestrial methane is produced primarily by living organisms, it appears that the quantities detected on Mars could have come from other processes.
I’m always happy to see potential evidence for extra-terrestrial life (especially intelligent life), however unlikely it may be. I’ve got a deep-seated hope that we’re not alone in the universe and I suppose that I’m always on the lookout for something to confirm this. Unfortunately, I’ve yet to find anything that doesn’t fall foul of either Occam’s Razor or my built-in bullshit detector. The jury’s still out on this one.
If we do find life on Mars, the next question will be whether or not it’s a long lost cousin, or an unrelated family. Mars and Earth have exchanged matter in the past, so it’s not beyond the bounds of possibility that someone small once hitched a ride. The discovery of ambiguous structures inside a meteorite from Mars some years back fuelled speculation that micro-organisms may have made the crossing, but the evidence was controversial.
Without wanting to reduce the importance of discovering (comparatively) close relatives elsewhere in the solar system, I’d hope that any life discovered on Mars proved to have evolved independently. Although we’d not be greeting our alien peers, this would imply that life is fairly common and would provide support for the more optimistic values assigned to variables in the Drake equation (ne and fl in particular), which in turn would make the Fermi Paradox more mysterious. And I’m a fan of mysteries as well as aliens, so that’s no bad thing in itself.