Woo! A subject dear to my heart.
I tend to believe in the seeding theory, although for me it's not so much that Star Trek concept of an ancient alien species passing through seeding genetic material (a plot device they used to explain all the humanoid species that appear in the show)... I tend to think of it more as, if it's even remotely possible that life can develop and survive, it will.
And if there's one thing we've learned, it's that every time we think a place is inhospitable to any kind of life, we find some there after all.
I still believe we -will- find signs of life on Mars. It'll probably be ancient and fossilised, but we know mars had liquid water on its surface, and a thicker, warmer atmosphere in the past. I think when we get there we'll find that at some point there's been life there too.
The reason we haven't found it yet is that despite out best efforts it's like we're trying to prove there's chocolate chips in choc-chip icecream by dipping the tip of a needle into it. How many times is that needle gonna come back with only a tiny bit of icecream coating it? Does that mean there's no chocolate chips in there?
We really have to get there, on the surface and -explore-. We'll never do it as well as that through teleoperation.
In addition to Mars I think there's a damn good chance we'll find existing, living, and bloody fascinating new forms of life when we eventually get to Europa (one of Jupiter's moons) and make it through the ice crust to the ocean underneath.
Even Io, although a killer environment for us might turn out support life similar to what we find on earth in volcanos and around sulpher springs.
It's gonna be awesome... I just wish we'd hurry the hell up and get out there.
Instead we're wasting $175 Billion on the ISS, to do the same orbital experiments we've been doing for 40 years. We could have put a base on the moon for a lot less, and it would make a much better staging point for future missions then the ISS ever could.
And again with Mars, NASA's basing its strategy on a hugely expensive method of getting there when it could be done so much faster and cheaper... On my more paranoid days I get the feeling that they're just stalling. Like they don't really want to go at all. But even then it could only be managments position, not that of the scientists who really make things happen.
I could go on all day... But I'll spare you all. :)