After 2 months of development, Stardock has released the first public update to WindowBlinds 3.

Version 3.1 supports a new skin language dubbed Extended Visual Styles (UIS1) that are literally twice as vast as XP's visual styles, work on every version of Windows, and are more compatible (downside is that they aren't nearly as powerful as UIS2 skins which is what most skins are done in).

Here is an article that talks about the new features and how skin authors can make the most of them:

http://www.windowblinds.net/wb3/wb31.html