There is a wonderful book called Molecules at an Exhibition in which the author does interesting profiles of compounds that appear in everyday things or situations, as well as unusual compounds like sarin, an extremely potent neurotoxin. As I was reading it, I noticed that he would mention the LD50 of almost every one, in sort of a morbid kind of way. I mentioned it to my cousin, who is doing a PhD in biophysics, and he said that it's one of the first things that chemists tend to ask about a compound, as in: "Cool, what's the LD50?"
OBTW, a lethal dose of caffeine is about 10 grams. That's around 100-200 cups of coffee, depending on your body mass, and how strong you like your java.