Dave Hyatt Tim Hatcher announced last night that the latest nightly builds of Safari now include a new tool for web developers to view DOM and CSS elements/attributes on a web page. I tried it last night, and it's excellent - even better than the one built into Firefox. You just right-click anywhere on a page, and a contextual menu item will let you "Inspect Element". This is perhaps more intuitive than Firefox's "enter a new mode, then click somewhere on the inspected page" method of visually selecting an element to inspect.
Here's a screenshot of the fancy new inspector, being used to debug a CSS problem I was having with the text in the header of my blog:
Update: I spaced on the author of the post. I guess I still think of the WebKit blog as Dave's old Surfin' Safari blog. It ain't, and there are multiple authors on the new WebKit blog. Oops.