Here's an interesting online calculator. It determines how much you would need to consume of your favorite caffeinated beverage for it to kill you.

Apparently, I am 1/50th of the way to kicking the bucket. Why, it would only take 98.31 more cups - mere gallons - to cause my demise!
Of course, it only takes a few pints of sea water to drown, but that's not the point. I don't willingly ingest sea water on a daily basis. I guess if I ate 12 whole turkeys, that'd probably kill me too. So you there, with your seventieth cup of espresso - you've got one foot in the grave already. Put it down!