Just in case you missed it the default theme in WordPress 3.0 has been updated to version 1.1. If your running WordPress 3.0 you should find an update indicator in your admin panel under Dashboard > Updates.
So when I saw this update a couple of days ago I went off in search of what was updated. Unfortunately there is not a changelog in the WordPress.org Themes Directory and a quick search did not yield very much at that time.
However, today when I made that same search I finally got some results and although it is not a changelog with a detailed listing of what has been updated it is from one of the WordPress Devs, Andrew Nacin and appears in the WordPress Support Themes and Templates forum:
Hey all —
The only real change is that I removed the half-baked code using the wp_title hook in order to customize the page title, and instead the code was moved back into header.php and simplified a little.
I can call it half-baked because I was the one who wrote it. It interfered with some plugins and so we yanked it. Twenty Ten is also likely going to be picked apart by up-and-coming theme developers, and I didn’t want my inventive technique to gain any traction. (I’d much prefer we introduce a replacement wp_title(), which you’ll likely see in a future release.)
We also made a few minor changes to attachment/media styling and markup. Just some tiny improvements for a few edge cases.
There’s a ton of other small changes in there — style.css for example — but they’re all stylistic. (Ha! — get it?) We alphabetized the CSS properties because that’s what the theme guys like. 🙂
I see Mo already posted the full diff. If you’d prefer for your head to not explode, here’s the log of commit messages:http://core.trac.wordpress.org/log/branches/3.0/wp-content/themes/twentyten/.
Hope that helps.
Nacin
So it seems to have been a general clean up and tweaking of the theme. If you desperately want to see the specifics then you can check out that last link he provided – there is a lot of detail there and personally makes my head hurt 
.
It is good to see that there is an intent to make this theme work with all the third party stuff that is out there. I think a big part of WordPress success is the attitude and desire of the devs and other contributors to make it the best it can be.
Keep up the great work everyone.
the Twenty Ten is written in HTML5, right?
Yes it is:
http://core.trac.wordpress.org.....=15262#L11
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It is written in HTML. It uses an HTML5 doctype.
I upgraded 2010 yesterday, no problems. ironically enough I started using the “Kirby” theme as soon as it was released. I found it to be an excellent theme that could be customized easily and didn’t load down the server with a bunch of bloated code. Then WordPress.org chose it as the new default theme for WordPress.
I always knew I had good taste.
I think a big part of WordPress success is the attitude and desire of the devs and other contributors to make it the best it can be.
I totally agree with this. WordPress is a community of people working together for the better.
I haven’t updated my sites from 2.9.2 yet. When I upgrade them to 3.0.1, will this latest theme come with it?
This theme is so clean, really good to learn. Btw I just made a translation of this theme to spanish, I’ll leave you the link in case one of your readers may benefit from using it.