Long ago a primitive agricutlural people tried to eke out a living in the shadow of a volcano. Nobody knew what made the rains come and the crops grow, and nobody understood why the volcano would erupt periodically and destroy everything they had built. The people had no choice but to rebuild what the lava had destroyed, for they lived on a small island, and had no other home. Furious efforts were directed at propitiating the evil demons in the volcano by sacrifices of animals and even children, and furious efforts were made to please the gods of rain and fertility, by incantations and magic codes.
A much respected priesthood of the volcano as well as high priests of fertility and rain, and oracles came to be established.
The practitioners of search engine optimization are in many ways similar to these ancient people. Our fortunes are in the hands of powers beyond our control. An arbitrary and unancounced decision, or even an error, by a minor archangel or demon in the Google or Yahoo! pantheon can wreck our livelihoods. The oracles of Yahoo and Google and Live Search speak to us in riddles, and the high priests mutter incantations. Not surprisingly, a whole lore of search engine optimization wizardry has sprung up. That doesn't mean SEO is all a myth, but it does mean that a lot of half truths and untruths and uncertainties are believed by many of us to be fact. I have devoted a section of the online SEO handbook to Search Engine Optimization (SEO) Superstitions. They range from outright fibs like Search Engines are case sensitive to plausible but possibly untested propositions, like the idea that there is a Penalty for link URL Variations. All information in those pages is subject to the whims of software engineeers at different comanies, and to empirical testing - package was full when shipped. Contents may have settled in shipping.
Here's the whole list for now, below. If you have any additions or comments, let me know (that's what the comments are for below). I may discuss some of these separately in the future.
Meanwhile, don't forget to say your incantations and paint the computer blue against the evil eye.