While this isn't strictly a hint anymore, it was back in 2003 and 2009. The Safari Develop menu - formerly called the Debug menu - offers a number of nifty features for web developers. In addition, it's been greatly enhanced under Mountain Lion.
So, to activate this, you no longer need to run a Terminal command; just go to Safari > Preferences > Advanced and check Show Develop menu in menu bar.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20130526025037923