Yah, that's the std Saganist rationale that life is common, early start on Earth, etc. that the space cadet crowd has touted for decades. However, if you read the biologists, not the pro-space physicists and astronomers, many if not most state that from what we know about what it takes to form a self-replicating org that can hold itself together (cell wall) while ingesting foodstuffs thru the wall and so on, all the just so arrangements of proteins that enable this wondrous feat, the improbabilities COULD exceed all the stars and all the 10s of billions of years of the universe. Both laypeople and scientists think that numbers like 10exp23 or so stars in the visible universe and 10exp 10 years are big numbers but it's short by orders of magnitude if the initiation of life is a ~10exp-60 or so event as several cell biologists contend. Biologists should know more about this than astronomers.

I think the chance of first finding strong evidence of extraterrestrial life is greater extrasolar. We aren't gonna fund and fly ice drilling missions to Europa or Enceladus in the next 2 decades, probably far longer given people's insatiable demand for govt funded social services. I'm beting there's no life in Mars' subsurface. So, our best odds of detecting life is via a TPF style spectroscope detecting active biology via atmospheric spectra, in the 2030s or thereafter. I think the 1st gen TPFs in the late 2020s won't be able to 'see' Earthlike planets further than ~50LY or so, beyond which I think statisticly the closest ones will live. Long before that, possibly by 2011 or so, Kepler will tell us the statistical frequency of HZ orbiting terrestrial planets. If they're common, the current spec TPF has a shot.