[sc]

The Web Inspector is actually part of WebKit itself (the rendering engine). You can get any improvements that happen there and between the chrome (HTML, CSS, JavaScript) by downloading WebKit nightlies: http://nightly.webkit.org

This update is for Safari itself, which is the UI/chrome.

[icefox]

As it is part of WebKit it on Linux you can play with the inspector using Arora

http://code.google.com/p/arora/wiki/Screenshots