I'm a couple of days late linking to this, but if you haven't seen it yet Matthew Jarpe, who is a biologist (biochemist?), has a good post on the origin of life on Earth.
One of the interesting things is that Matthew is of the opinion that life is likely to show up anywhere that liquid water is around for any significant period of time. I have seen wildly diverging opinions on this, all from knowledgeable scientists. But Matthew makes a good case.
Obviously, as a scifi writer, I'm inclined to like the idea that life is common, though I don't know enough to say anything for or against us. Obviously it raises the question of the Fermi Paradox ("Where is everyone?"). But just because there's a lot of life, doesn't mean there's a lot of intelligent life. And I can't find the link now, but I have read some people recently saying that getting radio signals from aliens further than our near terrestrial neighborhood wouldn't be so likely, unless they were specifically trying to contact us.
In any case, I say the more aliens the better! Except for the kind that like to eat us.