Updated 2009-06-09: This post is for the Safari 4 beta and will not work with the new Safari 4 released yesterday at the WWDC keynote. I’ve had a look through that release and can’t see any way to revert the address bar, etc sorry.

Having a quick poke through the new Safari binary yields the following strings:

$ strings /Applications/Safari.app/Contents/MacOS/Safari | grep DebugSafari4
DebugSafari4TabBarIsOnTop
DebugSafari4IncludeToolbarRedesign
DebugSafari4IncludeFancyURLCompletionList
DebugSafari4IncludeGoogleSuggest
DebugSafari4LoadProgressStyle
DebugSafari4IncludeFlowViewInBookmarksView
DebugSafari4TopSitesZoomToPageAnimationDimsSnapshot
DebugSafari4IncludeTopSites

NB: Run these commands in Terminal.app and then you need to restart Safari for them to take effect.

DebugSafari4TabBarIsOnTop

This moves the tab bar back where you expect it to be:

$ defaults write com.apple.Safari DebugSafari4TabBarIsOnTop -bool NO

DebugSafari4IncludeToolbarRedesign and DebugSafari4LoadProgressStyle

When both set to NO it restores the blue loading bar behind the URL. Also puts a page loading spinner in the tab itself, which looks odd with the new tabs.

$ defaults write com.apple.Safari DebugSafari4IncludeToolbarRedesign -bool NO
$ defaults write com.apple.Safari DebugSafari4LoadProgressStyle -bool NO

DebugSafari4IncludeFancyURLCompletionList

Switches off the new URL autocomplete menu and goes back to the original one.

$ defaults write com.apple.Safari DebugSafari4IncludeFancyURLCompletionList -bool NO

DebugSafari4IncludeGoogleSuggest

Turns off the new Google suggest menu.

$ defaults write com.apple.Safari DebugSafari4IncludeGoogleSuggest -bool NO

DebugSafari4IncludeFlowViewInBookmarksView

Removes CoverFlow from the Bookmarks view entirely. (Credit to Erik)

$ defaults write com.apple.Safari DebugSafari4IncludeFlowViewInBookmarksView -bool NO

DebugSafari4TopSitesZoomToPageAnimationDimsSnapshot

Disables the dimming when you click on a Top Site and it scales the screenshot up to fill the screen.

$ defaults write com.apple.Safari DebugSafari4TopSitesZoomToPageAnimationDimsSnapshot -bool NO

DebugSafari4IncludeTopSites

Disables Top Sites feature completely.

$ defaults write com.apple.Safari DebugSafari4IncludeTopSites -bool NO

Undoing changes

Just run the defaults command with the delete flag for the appropriate key you wish to delete.

$ defaults delete com.apple.Safari <key>

NB: Don’t include the -bool NO at the end, it just requires the key (eg: “DebugSafari4IncludeGoogleSuggest”)

Update 2009-02-26

Jools points out in the comments how to reset the recent searches in the google search box.

Update 2009-05-26

Lowell’s kindly created a Mac OS X application to edit these settings without using Terminal. http://github.com/cocoastep/tweaky

Update 2010-11-18

Patric has kindly translated this post into Belorussian and posted it on his site.