Nick Bostrom writes an interesting essay on anthropic observations, as usual. I agree with him that the answer to Fermi's "paradox" --- "why hasn't spacefaring life colonized our entire universe in ways we can detect" --- is that there isn't any.
But I think he misses a powerful argument that the "Great Barrier" to spacefaring life is the difficulties in our past, not the dangers in our future. It seems that if current progress continues, we're at most hundreds of years away from developing self-sustaining, space-capable artificial life --- AI, if you like --- even if we take the brute-force approach of brain simulation. It's hard to think of inevitable catastrophes that could wipe out all of a multitude of space-based intelligent machines with reproductive capability, even they were all confined to our solar system. Even if we don't make it to that point --- and I will not be surprised if we (or God) write an end to our history --- since we made it this far, given enough other civilizations one of them would be luckier and make it all the way, and go on to colonize the universe in observable ways.
But apparently they haven't.