Alongside the OS X Mountain Lion developer preview released today, Apple has also pushed out Safari 5.2 for Lion to developers. The update brings a number of new features that will be included with Safari in OS X Mountain Lion later this year.
Among the new additions are a unified address/search bar, new persistent Reader icon that is blue when available and grey when inactive, and new URL styling to highlight the domain the page is on while deemphasizing other aspects of the URL.
Apple has not said when it plans to release Safari 5.2 for OS X Lion to the public, but it will presumably do so alongside OS X Mountain Lion in "late summer". Apple just recently began seeding Safari 5.1.4 to developers, and the company will likely continue with the 5.1.x line on Lion until the Mountain Lion launch.
Source: Mac Rumors
Screenshot featuring the new URL bar: