Dashboard is nice, but how DO I make Safari sidebars?

Dave Hyatt said something interesting about the new dashboard widgets:

Just to prove a point that there are many ways to think about this new feature, here's another take on what Dashboard is. From a browser geek's perspective, the Dashboard is a collection of HTML sidebar panels liberated from the browser window and placed anywhere on your screen. The "Web pages as widgets" concept is really just a logical extension of the Web sidebar panel metaphor fused with Exposé.[...]
However the sidebar metaphor suffers from usability problems, such as the inability to scale up to many panels as well as being constrained by the browser's window width. It's also hard to view multiple panels at once. The panels are also tied to a particular application (the browser) despite frequently having no connection to the application itself.

Which makes sense for sidebars that are decoupled from the current page context. However, what is missing here (and as far as I could tell at WWDC last week, is not available at all in Safari) is a way to put a sidebar in the browser that is informed by the page context therein and can interact with it. As Hyatt says, this is possible in IE on Windows, and in Mozilla derivatives. Can we do this within Safari, using Dashboard or AppleScript, or anything other then hacking the nibs inside Safari itself?