This looks nifty and all, and I agree that their two "options" (edit -> browser -> reload vs. Firebug cut-n-paste) are indeed two options that many people consider, but they seem to have left out two other options that solve this problem quite elegantly, at least for Mac users:

1) Coda has real-time CSS editing built-in, and you can relatively easily fire up multiple windows to edit in a "real" editor (if you consider Coda a real editor) and view changes in real-time as you type

2) CSSEdit does one better -- you can edit using their editor and see changes in key-by-key realtime in their preview window. OR, and this is how I've settled on working, you can edit files using the editor of your choice (MacVIM, for example) and still see changes instantly upon save in their preview. So it reduced the need to reload the browser (saving half the steps). Now it's just a matter of make changes, Cmd-S (or however you save in your editor of choice) and it's all updated in real-time.