How to revert Safari 6 Web Inspector?
The new Web Inspector was made to be a bit closer to Xcode. 

There is no direct way to get the old one back, without reverting to other means. For example:


running Lion in a VM (to run an older Safari).
Running a nightly build of WebKit - but this may only have the new inspector
Using Chrome (while still WebKit, it still uses something that seemed closer to me like the old inspector). 


So no, at this time, it doesn't look like its possible to revert back to an 'older' version of the inspector. The best bet would be to submit bugs at http://bugreporter.apple.com. If it is missing features that the old one had, possibly future revisions would bring some of this back.