For a detailed discussion and examples, this is the thread you need over on Google Earth Community.
It would be great if Google or some group or organization could throw some more attention on this issue in regards to KML. KML standardizes the ‘where’ and ‘when’ information within a popular and easy xml standard and it would be interesting to see the ‘what’ part of this data stream standardized also. Separating data content from data display into a more standardized xml schema would allow KML to enable better end user data reuse, aggregation and styling needs.
As far as I understand it, KML is a tradeoff between ease and power. For a fully descriptive mark-up language that properly separates style from content, try GML, though it is harder to use.