I've installed the Safari 3.0 beta, and so far I like it. While I was trying to dissect some CSS - JavaScript, I suddenly remembered I'd read about enabling a pretty neat Web Inspector tool in one of the nightly builds:

defaults write com.apple.Safari WebKitDeveloperExtras -bool true
Launch Safari, and control-click somewhere on a web page. You will see a new Inspect Element entry in the contextual menu. Select it, and it will open up the Web Inspector and refocus to the node under your cursor.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2007061303320554