Apple's yearly developer conference should see iOS 8, OS X 10.10, and likely some hardware.
Mac OS X Theme Change in Leopard Seed 9A410
Edit: Images removed per Apple Legal.
Images originally posted on Hackint0sh.org. Images are mirrored here. Alternative screenshots are posted on Flickr.
Apple also announced today that Leopard would be delayed until October, so these changes may not represent the final user interface.