I'm working through Kurzweil's book, The Singularity Is Near.  An interesting book, with lots of cool stuff from recent findings about the brain.  See http://www.kurzweilai.net/ or http://www.amazon.com/gp/product/0670033847/sr=1-1/qid=1154721252/ref=pd_bbs_1/103-0343898-9860653?ie=UTF8&s=books.

Kurzweil argues that the reason SETI has failed is that no one is out there, because if they were, a society only a few decades more advanced in technology than ours would have made one hell of a noticible effect.  He discounts the argument that technology is fatal because even if technology were usually fatal (i.e., blowing up, poisoning, or infecting the whole world), out of thousands of tries surely some race on some planet would get lucky.

But earlier in the same chapter he jiggled the numbers that folks who are optomistic about alien life use to predict thousands of them out there and came up with the expected number of civilizations who are technologically advanced and use radio waves to communicate as about 1.25, and, as he says, we already know which one that is.

But jiggling the numbers so that you fall between the SETI optimists and his pessimistic number, what if technology kills 99.99% of races that develop it, only a few hundred have managed to do so, and it killed all of them?

In the Cold War we could have killed the planet with nukes, and nuclear proliferation has not gone away.  Bioterror seems to be a growing possibility.  And nanotechnology means that a malfunction or a programming error -- the equivalent of an infinite loop -- could result in unchecked nanobot replication, until the world was buried under gray sludge.

I think we're going out with a bang rather than a whimper, and probably in this century.  Hope I'm wrong about this.