The dude behind xkcd tackles some strange questions in this delightful book. While all of the questions are fairly absurd, they also range widely from dumb (What is Yoda's Force power output?) to the potentially profound (If everyone on Earth vanished, how long until the last artificial light went out), as do Munroe's answers. Not every absurd question deserves and answer, and a few intercalary appetizers appear from time to time with questions that he didn't see fit to answer, but are usually amusing/horrifying (e.g. "Would it be possible to get your teeth to such a cold temperature that they would shatter upon drinking a hot cup of coffee?")
Although he occasionally plays fast and loose -- often by necessity given the utter absurdity of some of the questions -- most of the answers are based on good solid science. And there are plenty of interesting factoids buried here and there, like the fact that the greatest contributing factor to sea level rise is not melting ice-sheets, but actually the thermal expansion of water, or if you printed out all of Wikipedia, the paper would occupy a volume of about 300 cubic meters.
He comes up with a couple snappy answers to some too-frequently-asked absurd questions. Like noting all the positives that would occur if the Sun suddenly went out. Forget about the improved satellite service, and imagine the advances in international trade and communication since there will no longer be any need for time zones. Or the question about people gathering in one place and jumping at the same time. After the anticlimactic result, Munroe describes the cataclysm that occurs as everyone tries to go home again.
An enjoyable and pretty fast read (plenty of pictures!). If you need to know whether you can build a bridge out of Legos that spans the Atlantic Ocean, or need to know what the map of the Earth would look like if water started magically 'draining' out the bottom of the Challenger Deep, this is the book for you.