I'd much rather wade through the html and css in a github project then try to decode the ramblings of a hastily written tutorial.
I wrote something very similar a couple weeks ago - going to go back and apply some of the nice visual effects this contribution shows - very appreciated!
The sum of these tiny 'do one thing and do it well'-projects improve our collective developer-lives tremendously.
This one may be just 3 lines of CSS. But it has to be the right three lines or it will break on some browsers. And those 3 lines might change in the future to accomodate new browsers.
tldr; Code sharing is good. Do it.
What's the rationale for CSS only? Considering progress is about waiting for things to happen, what is the timing based on? What triggers updates or changes?
I think Webkit has a similar approach, although I don't know if it provides as much freedom in styling as the -moz-version.
I guess for usability there should be text inside or underneath saying the % progress? (In which case it'd still be XHTML for content and CSS for presentation)
<div class="progress" style="width: 40%;"></progress>
Also seconding the simplicity of the project (i guess new years eve is a low-volume time of the year for submissions, but i wouldn't have expected this to be #5 on the front page.. must have hit all the right buzzwords.)
(See: https://developer.mozilla.org/en/CSS/animation for further information)
edit: anything you particularly like about him?
Also, sparklines. :)