1. Base Font, Text & Colors
2. Layout
3. Post/Page Content
4. Comment/Pingback Properties
5. Search Bar/Box Properties (optional)–NONE
6. WordPress Calendar
7. WP-Specific Classes

It was my attempt at being a hybrid between pure style organization by html structure, and structuring it around design aspects. The way I see it, you will always have div IDs for each area of the site. The calendar function that wordpress provides is optional, so you dont always need 6 or 7, but it is easy to remove if that is the case.

Most widgets and plugins that have styling rules use a css file within the plugin/widget folder so you almost never need to add anything more. Either way, this organization has helped me in knowing all the kinds of styling I might need for wordpress but they are organized in such a way that I can abstain from including areas I dont need in a specific theme such as the wordpress calendar styling.

You say: "If there are only two values, it is assumed to be top and bottom."

This is actually assumed to be top/bottom and left/right.
margin: 5px
-> T/R/B/L: 5px

margin: 5px 10px
-> T/B: 5px - R/L: 10px;

margin: 5px 10px 15px
-> T: 5px - R/L: 10px - B: 15px

That's how shorthand is used.
Nice article :)

Pieter.

Thanks for reminding me

It's Andre from Brazil. Those are nice tips, but do you use any kind of tool to join and compress the CSS files?

Thanks!