Apple's yearly developer conference should see iOS 8, OS X 10.10, and likely some hardware.
Snow Leopard to Bring Unifying 'Marble' User Interface?
Based on our sources, however, Apple will apparently use Snow Leopard's release to tweak the overall user interface for Mac OS X and unify it across applications. Exact details of the theme changes have not been made public, as the current developer seeds for Snow Leopard still retain Apple's existing Aqua theme. The new theme will likely involve tweaks to the existing design and perhaps a "flattening" of Aqua in-line with Apple's iTunes and iPhoto interface elements.
The codename for the new interface is said to be "Marble" -- though that seems likely to be an internal codename only. John Gruber had also hinted at such changes in a pre-Macworld prediction piece and had independently heard the codename "Marble".
Apple's Snow Leopard is rumored to be released as early as the first quarter of 2009.