Dave Hyatt, the guy behind Safari and WebKit, clarifies various possible components of a Dashboard widget.
On an unrelated note I was wondering if Dave could also shed more light as to what Safari can do with RSS feeds: Steve's keynote seemed to imply Safari RSS Search would "scour the internet" for feeds relevant to terms you specify, which struck me as odd. I assumed Steve meant would "scour feeds you have subscribed to", which makes more sense and is what's written on the tiger safari page. I might have misunderstood the keynote, but it did really seem Steve was confusing himself there, maybe I was the only one confused. The distinction is important though: from what I understand Safari can only give you matching results for feeds you have already made the conscious decision to subscribe to. It won't show you information from everything that's on the Internet. Those searches are essentially "local": 1) feeds are periodically retrieved to your hard drive, 2) RSS Search scours what's on your hard drive.
It might be interesting to look at services such as PubSub.com, which already indexes bazillions of blogs and RSS feeds. Also, yahoo search exposes an RSS Link for sites that offer an RSS feed. Why's Google not doing that. hmph! Were any of these guys able and willing to offer some sort of XML API, Safari could plug into it to scour the web for any topic covered via RSS feeds, in more-or-less real-time, well at least in PubSub's case.