Mac OS X 10.6.3 Build 10D561 has been released to developers less than a week after the previous build. Not a great deal has changed since the last build -- iPhoneinCanada has the specific details on this latest build, which include refinements to OpenGL and 64-bit logic. Since this sixth 10.6.3 build follows so quickly after the last one, it's a good indication that an official release of 10.6.3 is imminent.
10.6.2 arrived on November 9, 2009, and, like the forthcoming 10.6.3, was primarily a bug fix update for Snow Leopard. 10.6.3 should be out any day now in Software Update complete with those always-informative release notes, including my favorite: "increases reliability and improves compatibility and security."