As you might remember late last year, Apple released a sneak preview of Mac OS X 10.7 codenamed Lion. A major aspect of what was unveiled has already been implemented with the Mac App store. There hasn't been much news of late but there has been rumblings inside Apple that would seem to suggest that they are now using Lion widely internally and not just among the dev team. A developer beta is expected by the spring with the final penciled in for late summer.
With Lion, Apple's primary goal is to shift Mac OS X toward the iOS interface paradigm. Although it is doubtful that this will happen with Lion by itself. We wouldn't be surprised if we eventually see hybrid Macs which combine touch screen interfaces with traditional form factors. Through this process they hope to further bridge the gap between the different devices that are utilized by consumers, which may within 5 years eventually see Mac OS being amalgamated into the iOS platform as a unified OS across all of Apple's devices.
This can be evidenced by Apple's UI changes which have placed a heavier emphasis on the desktop and putting applications in it as opposed to the traditional folder in the dock/finder.
Apple is also busily testing the next version of Snow Leopard 10.6.7 but this is being tested independently from Lion.