Totally thread-jacked now, but if you guys like the "What-If" thing, you might be interested to know that the creator, Randall Munroe, is releasing a book in September that will be a collection of those essays that haven't been published before as well as some of his favorites. He updates What-If at least weekly, it seems, if it's not quite as regular as his "day job" of xkcd.
Anyway, linkage for book:
What If?: Serious Scientific Answers to Absurd Hypothetical Questions - Kindle edition by Randall Munroe. Professional & Technical Kindle eBooks @ Amazon.com.
/tk