I agree with you there are several mistakes in the "Customizing Locators in ArcGIS 10" document that have caused me to waste a significant amount of my company's time (and therefore, money) chasing down the wrong approach. For example:
I think there is a lot of power in the geocoding engine, but without documentation, it's almost completely useless unless you live in the US and can use the built-in locator styles. You're not the first person to ask for better documentation, but it doesn't seem that this issue is ever going to be addressed, frankly because no-one at ESRI seems to care too much about it.
I have wasted more time trying to get locators to work properly than I have on any other aspect of ArcGIS. This feature is vital, and the lack of proper documentation is astounding. In my opinion, this is the weakest aspect of the ArcGIS suite by a significant margin.