How do you remove Safari 6 on Mac OS X 10.7.4
To downgrade Safari 6 on OS X Lion (10.7.4) to Safari 5.1.7:


Use Time Machine to have a fresh backup!
Get Pacifist.
Get Safari 5.1.7 for Lion here (apple.com) 
or here (mirror).


$ md5 Downloads/Safari5.1.7LionManual.dmg
MD5 (Safari5.1.7LionManual.dmg) = 504bdd1629f660084725d9883629f58e (same for both download links)


Quit Safari if running.
Install Safari 5.1.7 using Pacifist. Select "Open Package", choose the 5.1.7 dmg from step 2. Click on the "Contents of Safari5.1.7LionManual.pkg", Click "Install" on the toolbar, Choose "Yes" or "Replace" when asked (select the box for all continuous questions).
Open a new Finder window and press Command ⌘+Shift ⇧+G (Or menu "Go" -> "Go to Folder...").
Paste /System/Library/PrivateFrameworks/ in the goto field.
Rename the "SafariServices.framework" folder to "SafariServices.framework.disabled" (You will be asked for your admin password).
Use Finder go to again for /System/Library/StagedFrameworks/Safari/ folder. 
Rename the "Safari.framework" folder to "Safari.framework.disabled".
Rename the "WebInspector.framework" folder to "WebInspector.framework.disabled".


  The last one (WebInspector.framework) and possibly the first one (SafariServices.framework) don't really need to be disabled; Safari 5.1.7 will start anyway (at least for me), but since they weren't there before 6.0, I disabled them, too.

Launch Safari.
If you're happy with your newly downgraded Safari, you might safely delete those .disabled folders/frameworks. They will be reinstalled if you ever choose to install Safari 6 again. Look for the disabled frameworks (e.g. "SafariServices.framework.disabled") and move them to the Trash. You will be asked for your admin user's password again.

If it doesn't work for some reason, you can re-install Safari 6 from Software Update.
Run Disk Utility and Repair Disk Permissions.