[BlueTemplar]

Of course it's an estimate, but I doubt it's wrong by more than 1-3 orders of maginitude...

The most recent article I could find after a quick search is from 2003:
http://www.cnn.com/2003/TECH/space/07/22/stars.survey/

http://hypertextbook.com/facts/1999/TopazMurray.shtml
http://astronomy.swin.edu.au/~gmackie/billions.html

Looks like the author has the same point of view as me about life in the universe:
http://www.thekeyboard.org.uk/Extrat...ial%20life.htm