/dev/trouble
Eric Roller's Development Blog

To enable the debug menu, type in the Terminal application:

> defaults write com.apple.safari IncludeDebugMenu 1

To use Yahoo instead of Google in the search bar, you can hack the Safari binary, for instance with the vi text editor:

> vi /Applications/Safari.app/Contents/MacOS/Safari
vi>/%@.google.gom

Then replace these strings (must be the exactly the same length!):

http://%@.google.com/%@?q=%@&ie=UTF-8&oe=UTF-8
http://%@@search.yahoo.com/%@?p=%@&ie=UTF-8&a=

[Update 2014-12-25] NB. Since GateKeeper was introduced, you can no longer hack the binary. Safari would no longer be allowed to launch.