Apple has reportedly begun seeding Build 10D522 of Mac OS X 10.6.3 to a limited set of developers, marking the first official beta version of the third maintenance release for Mac OS X Snow Leopard. According to those familiar with the release, Apple has addressed approximately 225 issues in the update, which reportedly weighs in at roughly 666 MB.
Apple documents four remaining known issues in the current build, related to application updating, Displays preferences, iTunes hangs, and ColorSync Utility Filters.
Word surfaced nearly a month ago that a 10.6.3 beta release was imminent, but Apple apparently decided not to push any testing versions to developers until after the holidays. Apple's last update to Snow Leopard, Mac OS X 10.6.2, was released nearly two months ago.