Media event set for September 9, launch likely ~10 days later.
Apple Releases New OS X Lion Software Update for DP4
Apple seems to be putting the final touches on OS X Lion which is set to launch in July. They have pushed out a new software update for developers who are running the Developer Preview 4 that was released at WWDC.
There's no word on what has changed between versions. OS X Lion will be launching sometime in July for $29.99 via the Mac App Store.
Update: It's All Tech posts some of the changes found in the latest release. Perhaps most notable is that this build is not the final since there is still placeholders for some of the videos: