As input managers are in danger in Safari 3.0 and later versions, it might be useful to know that a type-ahead search feature that emulates Firefox can be enabled in Safari using a fairly simple hack that involves native OS X tricks.
To do so, quit Safari and go to System Preferences » Keyboard & Mouse » Keyboard Shortcuts. Click the '+' to add a new shortcut, select Safari as the Application, Find... as the Menu Title, and a temporary (and arbitrary) shortcut as Keyboard Shortcut. (Note that this field does not allow a simple entry, such as '/', but instead requires a modifier key like Command or Option.)
Now go to ~/Library/Preferences and edit com.apple.Safari.plist. (You may be able to just double-click and open the plist in Property List Editor if you have Xcode installed.) Find the NSUserKeyEquivalents entry and edit the string entry for Find..., replacing the arbitrary shortcut you entered earlier with /. This will remove the need for a modifier key, and allow / to activate search.
Now relaunch Safari and type /; you should see the Find box appear, emulating the type-ahead search in Firefox.
[robg adds: Queue user fds offers up a one-line Terminal alternative to creating this shortcut: defaults write com.apple.safari NSUserKeyEquivalents -dict-add Find… /. He also points out the downside of this modification: if you're in a text box, you won't be able to activate the search box, as the text box will accept all the '/' keystrokes, as it should. With the default of Command-F, you can use find even when a text field has focus.
If you'd like to undo this modification, and you used the long method above to create it, you can just delete the entry in the Keyboard Shortcuts list. If you used the Terminal shortcut, though, there won't be an entry there. You can either add it and then delete it, or this should work in Terminal: defaults write com.apple.safari NSUserKeyEquivalents -dict-add Find… @f.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20071212073849257