Are we Alone?

Well, time for me to put up another big-question post.

Fermi's Paradox has fascinated me for years, and an interesting in MITs Technology Review has reminded me of the topic. The interesting point of Nick Bostrom's article (registration required) is that he hopes that we find no signs of life on Mars. Bostrom suggests that there must be some bottleneck that explains why the galaxy (and the universe) is not teeming with life. He calls this restriction the Great Filter. If that problem is behind us, then there is a good chance our civilization will survive for a long time, while if it is ahead, then our chances of survival must be minuscule.
He concludes that:
If--as I hope is the case--we are the only intelligent species that has ever evolved in our galaxy, and perhaps in the entire observable universe, it does not follow that our survival is not in danger. Nothing in the preceding reasoning precludes there being steps in the Great Filter both behind us and ahead of us. It might be extremely improbable both that intelligent life should arise on any given planet and that intelligent life, once evolved, should succeed in becoming advanced enough to colonize space.
But we would have some grounds for hope that all or most of the Great Filter is in our past if Mars is found to be barren. In that case, we may have a significant chance of one day growing into something greater than we are now.

I found this an interesting way to think about the problem.
Even thoughI love Science Fiction and stories about galactic civilizations and alien species, the Fermi Paradox leads me to conclude that we are alone or nearly so.