I was just reading a Gadling blog post this morning where Heather Poole reviews Betty in the Sky With a Suitcase - the book, and in the blog it is revealed why you must put your seat in the upright position. Since I posted about that recently, I thought I would let you all find out for yourselves from the blog post.
http://www.gadling.com/2010/08/09/galley-gossip-a-funny-flight-attendant-book-betty-in-the-sky/
I also feel the need to add that I have not read the book, but I do listen to Betty's podcast and if the book is anywhere as good as the podcast you should run out and buy it now! Why haven't I read it if I say you should? I've been terrible at reading books lately (they take me months to read), so I'm being extremely selective about what books I buy, let along read.
