Custom Kubrick or Default Theme Headers are now live for wordpress.com users. Donncha has turned this function on in the Presentation Panel, and you can see it only if you are using the Default/Kubrick Theme. As mentioned, the Kubrick Header Switcher was developed by Andy Skelton for WordPress 1.6, the alpha-stage next version of WordPress.
I look forward to more of this kind of customization in the future as the program develops. Right now a lot of people are complaining because wordpress.com is so limited due to its lack of customization. That’s because most of these people have already had a taste and the experience of customizing their sites with the full WordPress version. And everyone seems to forget that wordpress.com, WordPressMU, and WordPress 1.6 is in the alpha testing phase. It hasn’t even reached beta testing. We wordpress.com users are living in a glorious Cracker Jack box. Every day we open it to find a new surprise!