Between all the stars of all the galaxies in the universe, the odds of there being other life besides us is amazingly huge. So high in fact, that the odds are likely greater then your having been born.
Not a technical source, but I liked the quote:
All of my ancestors (and yours) survived long enough to procreate against considerable odds – in a long, long line going back to a single [celled] organism. And, of course, each of my ancestors (and yours) which produced millions of sperm or hundreds or thousands of eggs were the focal point of a genetic jackpot in themselves.
The problem to keep in mind with SETI is that the time-frame for advanced life on a planet is amazingly small compared to the life-span of planets, star systems, galaxies, and the universe. Even worse - the further away we look, the older the source for any indication of life will be.
A signal reaching us from elsewhere in the galaxy could have been in travel for tens of thousands of years, which unfortunately puts a bit of a damper on having any hope to communicate. Factoring in the Inverse-Square Law, the distance from which one could discern an RF signal from background radiation is reduced significantly. If we are really lucky, we might find a signal within a hundred light-years or so; but that would preclude any chance for communication within our generations life time.
Somewhere out there is (or was) life in the right place, at the right time, doing the right thing, and having sent out a signal long enough ago and not too terribly far away. It may sound like the odds are stacked against us; but discovering life outside Earth would be one of the most amazing discoveries of all Humanity. It would change our culture, our science, our ways of thinking, and would give a much greater importance to both space and space travel.
While I still think that it’s entirely worth the effort to look for Alien life; it does help to keep some perspective. The nay sayers might claim that had there been life outside Earth, we should have seen it by now… but they don’t understand the scale and scope of things.