"3) Since you site Yeoman as the leading impact rate authority and he states the average interval for the entire Earth for Tunguska class objects is at least 100 years and only 10 % of the Earth's surface is densely populated (as opposed to areas like Siberia) impacts in populated areas should happen on average less than once every 1000 years. Thus, it is quite likely that colonization could be well under way before even a Tunguska class event hits a populated area."

From what recall he also said we are "due" for another Tunguska, since it's been about 100 years (not that the odds work this way- we could not have another for 300 years or 2 or 3 in the next 10 years). A point I really wanted to make is that since Apollo we haven't made too much progress towards colonizing space. If we continue "the program" how much progress can we expect in the next 30 years?
One way to look at most of our "progress" is it is due to NASA's failure. We have private launch today because the Shuttle failed- in number of ways.
A space station because the soviets/russian were beat in Moon race, then NASA percieved a station was needed- cause the soviets had one. Then proceeded to "catch up". There wouldn't be the current effort of privatizing of space if NASA was "working". Nor would Zubrin have a book and a cause if wasn't for NASA failure to move. You can't give this credit to NASA- it's despite their "best efforts".
So if socialism won't get us there, what will?
-gb