that a cats' tail is one of the best mood barometers?

The tail is part of the spine, is used for balance and serves an important role in communication.

An upright tail when the cat is standing or walking lets you know he is alert. When he flicks his upright tail at you, it's usually meant as a greeting.

A relaxed tail  in a cat is horizontal or somewhat down.

A lashing or thumping tail reflects irritation. If you are petting your cat when this happens, it's a good idea to back off.

When a cat is resting, an occasional twitching or sweeping motion of the tail mean he is still relaxed but alert.

A frightened cat will puff out the hairs on his tail (piloerection), so it looks more than twice his size.

A tail in an inverted "U" shape indicates that the cat is fearful and potentiaslly defensively aggressive.

A submissive cat will tuck his tail between his legs, trying to be as small and invisible as possible.

From "Think Like A Cat." How to Raise a Well-Adjusted Cat, not a Sour Puss. Pam  Johnson-Bennett. Feline Behaviorist.

 ... that the United States has become a nation of “cat lovers”? There are approximately 88.3 million owned cats -as opposed to 74.8 million owned dogs- and 56% of cat owners have more than one cat. And these numbers do not include the many stray and feral cats that continue to live within and around human communities.  

American Pet Products Manufacturers Association (APPMA).  

2007-2008 National Pet Owners Survey

... that even though cats and dogs are members of the order Carnivora, which includes a diverse group of animals that are all predatory, their evolutionary paths diverged more than 30 millions years ago and cats evolved as strict carnivores?  This means that they have existed for all these years by feeding almost entirely upon small animals, such as mice and voles. Because felines adhered to such a specialized diet throughout their evolutionary history, this has resulted in specific physiological and metabolical adaptations that manifest themselves as unique nutritonal requirements. As a consequence, there are some nutrients that cannot be made by their bodies nor can they be obtained solely from plants products; therefore, they require the consumption of animal tissue to meet those requirements. That is why cats are known as "obligate carnivores": they must have meat/animal tissues in their diets.

From "THE CAT. Its Behavior, Nutrition and Health."  Linda P. Case