I wasn't at first either and sought out these settings to revert back to the pre-4.0 way of doing things. There are plenty of copies out there of this, but I figured it'd be good for posterity to repost, just in case I ever easily want them again. As a side note, I used the first three of the settings on my workstation at home while my laptop for work I kept as the default redesigned settings. It's not so bad after a while. The only thing that annoys the hell out of me is when clicking on tabs I find myself accidentally moving the window around. Oh well, all in the name of 'progress'.

Move the tab bar back into the window:

defaults write com.apple.Safari DebugSafari4TabBarIsOnTop -bool NO

Move the "Add Bookmark" and "Stop/Reload" buttons out of the URL field:

defaults write com.apple.Safari DebugSafari4IncludeToolbarRedesign -bool NO

Restore the blue loading bar behind the URL field (yes, you need both of these):

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

Switch off the new URL autocomplete menu and use the original one:

defaults write com.apple.Safari DebugSafari4IncludeFancyURLCompletionList -bool NO

Turn off the new Google suggest menu:

defaults write com.apple.Safari DebugSafari4IncludeGoogleSuggest -bool NO

Remove Cover Flow from the bookmarks view:

defaults write com.apple.Safari DebugSafari4IncludeFlowViewInBookmarksView -bool NO

Disable 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

Disable Top Sites feature completely:

defaults write com.apple.Safari DebugSafari4IncludeTopSites -bool NO