Disclaimer (5/28/2013): Your mileage may vary using this procedure. At the time, I was downgrading from a beta version of Safari 6, and I was using OS X 10.7.3. At this point (May 2013) I have switched to Safari 6, as the Web Inspector has been improved tremendously.
If you are currently running Mountain Lion, or have installed a more recent version of Safari 6 (released anytime after Oct 2012) then you may encounter serious problems when attempting to follow these instructions.
So, I decided to downgrade back to Safari 5.1.7, because I prefer the old Web Inspector over that of Safari 6.
More importantly, though, it doesn't work AT ALL for debugging UIWebViews in Simulator. Apple has crowed much about Safari 6's Web Inspector, and how it will help developers debug more effectively – but in reality, it doesn't work at all (yet).
So, with no further ado, here's how to relieve yourself of Safari 6 and get your old software back.
Download Safari 5.1.7 for Lion.
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", then click "Install" on the toolbar. Choose "Yes" or "Replace" when asked, and wait for it to finish.
Disable the frameworks that were installed by Safari 6 (by renaming them). You will be prompted for your administrator password.
$ cd /System/Library/PrivateFrameworks
$ sudo mv SafariServices.framework SafariServices.framework.disabled
Disable additional Safari 6 frameworks (optional, but recommended):
$ cd /System/Library/StagedFrameworks/Safari $ sudo mv SafariServices.framework SafariServices.framework.disabled $ sudo mv WebInspector.framework WebInspector.framework.disabled
If it doesn't work, you can re-install Safari 6 from Software Update.
This tip has been adapted and simplified from this StackExchange thread