I knew that the 7 days of the week were named for gods, and I might have even known about the "7 days for the 7 planets" (of which the Earth isn't, and the sun and moon are), but if I had ever seen the explaination of how each day ended up with its name I certainly hadn't remembered it (until now)! And some of the examples in "How Do Conmen Get Rich?" really made me stop and think (in particular: Predicting the sex of your baby and The football con).
The sub-titular purpose of How Long is a Piece of String? is to reveal mathematics underlying every day life. As a holder of a Bachelor of Science in Mathematics I didn't find it terribly revealing in that regard (having already known it), but I think that it did a very good job of explaining the kinds of problems that various fields of math (or, since the authors are British, perhaps I should say "in maths") work on. In that respect, I think that this would be an excellent read for a college student who is a fan of math, but isn't sure what field they want to pursue.
If "Should I Phone a Friend?" spoke to you, you probably want Discrete Math or Economics.
If "How Long Is a Piece of String?" was the most fascinating, you want to study fractals.
If "Why Do Weather Forecasters Get it Wrong?" was titillating, Chaos Theory, or Cryptography.
(And most of the other chapters have an implied focus, as well, talk to your advisor/favorite math professor/head of the math department to see what your favorite implies)
If you're not mathematically inclined, but like to know what makes the world around you tick, you'll also probably find it an interesting read.