Apple has quietly posted an overview guide to Mountain Lion Server. The 25 page PDF document is available from Apple’s OS X Server Resources page, which barely references Mountain Lion at all. The generically named OS X Server Product Overview link in the page’s Documentation section, however, links to the new Mountain Lion Server product brief.
The overview guide is listed as being updated for June. That implies that it was deliberately placed there in advance of next month’s Mountain Lion release (as opposed to going live early by mistake). The guide primarily focuses on introducing the various features in Mountain Lion Server. While not in-depth, it definitely provides a sense of where Apple is going with Mountain Lion Server as well as with Mac and iOS management.