Yeah, great book. He's a good writer.
Here is some hearsay about the Drake equation: I just attended a conference in the Netherlands regarding the Cassini/Huygens mission, which is currently entering the Saturn system. Some of the people there where from JPL, where Carl Sagan worked back in the heydays of the Voyager and Pioneer space probes.
One of them was the chief scientist of the mission, and he pointed out an interesting problem which he said had come up when he had talked to Frank Drake. The left part of the equation, "N", is the number of civilizations in The Milky Way Galaxy whose electromagnetic emissions are detectable.
Now, after some 50 years of radio transmission, suddenly radio and television broadcasts are going silent. Most of it is now transmitted either via satellite or fiber optic cables. Both of these would be undetectable if you look for electromagnetic emissions.
The problem becomes whether the "window of opportunity" for finding civilzations based on the assumption that they actually make noise that we can detect is much shorter than what Frank Drake assumed.
I had never really thought of that before, but it is an interesting perspective. It could imply that the search for radio signals with the Arecibo telescope could be in vain (but we might of course never know that).
For the record, I think the Drake equation is a great idea and a masterful stroke. If it turns out to be flawed, it could still be repaired if we can find other ways to identity civilizations. The equation was constructed in a time period when electromagnetic emissions due to communication was the obvious thing to look for (since we caused a lot of it ourselves). Maybe other civilizations would stay with radio longer, while other would do it shorter.
The Drake Equation:
http://www.seti.org/seti/seti_science/
Tormod