Safari 4 Hidden Preferences

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