Restore previous Safari version from .SafariArchive.tar.gz Did that new Safari update (5.1) break something and you'd like the old version back? Thanks to Apple's prescient yet secretive engineers, there's a way. 

When Safari does an upgrade it saves the previous version in this location: 

/Library/Application Support/Apple/.SafariArchive.tar.gz 

To restore Safari, have tar to expand the archive to the root folder:

sudo tar -xvf /Library/Application\ Support/Apple/.SafariArchive.tar.gz -C /

To be complete, delete the receipt from /var/db/receipts, in this case it is the one for Safari 5.1:

sudo rm -rf /private/var/db/receipts/*

Reboot, since we've just replaced a whole bunch of public and private frameworks the OS uses. 

[crarko adds: I haven't tested this one. As always, have a recent system backup around just in case. This hint is not applicable to Safari 5.1 on Lion.]