Nearly every class I lead, I say that one could write several chapters on conditional formatting (maybe +Contextures Inc. or +John Walkenbach or +Helen Bradley might. Chapters that have detailed examples, screenshots and so on.
One thing that has been puzzling me is how to use the very pretty and eye catching effectiveness of conditional formatting with floating reference cells. - It's obvious how to conditionally colour a range against a fixed number (e.g. 50) or a fixed cell (e.g. $B$2) but it's more useful to compare say, 1990 figures against 2013 figures, row by row.
The user interface is not obvious for doing this and I just happened to see Susan Harkins's article on Techrepublic.
To further clarify the syntax, here's my screenshot: