Apple will introduce new versions of iOS and OS X at its annual developer's conference.
New Snow Leopard Build (10A261) Seeded to Some Developers
According to Macity's sources, the latest version does not appear to contain any noticable changes but does seem more stable (translated):
The interface has not been revised and currently there are only small changes in System Preferences, have been resolved a few bugs in the Finder and little else. According to the sources of Macity the impression is that this release is more reliable than those previously distributed.Apple has been rumored to be tweaking the user interface in Snow Leopard prior to its public release.
Snow Leopard is the codename for the next major revision of Mac OS X. Apple has said that they would be focusing on quality and performance in Snow Leopard. In particular, Apple has made it clear that there will be efforts to improve support for multi-core processors and GPU processing. These improvements will help developers more efficiently use these capabilities that already ship in Macs.
Update: Note: the update appears to be available to a limited audience at this time.