To be honest. With firebug's ability to tell me what line and css files the style on an element is coming from I don't find spending a lot of time on organization to have a ton of benefit.
While I love Firebug, I'd have to counter that organization with CSS is actually quite important (and does have its benefits!)
This is especially true when you're working either in a team environment or on a large site. The very nature of CSS (and how things cascade down) can become a nightmare when organization isn't taken into account from the start.
I agree completely, especially on a web app that is constantly growing. 2 on-the-job things that help me the most are:
1. Using the 960 grid system (or your preferred grid flavor)
2. Grouping by the following:
Body
Typography
Forms
(Other global stuff like links and buttons)
/* Layout Element 1 /
ID1 {}
ID2 {}
class1 {}
class2 {}
/ Layout Element 2 */
ID3 {}
ID4 {}
class3 {}
class4 {}
I also write my styles on one line, but that's just personal preference. I find it easier to scan down for the selector, then across for the property I want. I definitely don't do it for aesthetics or file size ;)
This is especially true when you're working either in a team environment or on a large site. The very nature of CSS (and how things cascade down) can become a nightmare when organization isn't taken into account from the start.