Previewed at WWDC, launching in the fall.
Mac OS X 10.6.8 Brings TRIM Support for Apple SSDs, Graphics Improvements [Updated]
Support for TRIM has been included in OS X Lion since its early developer builds, but Apple has apparently decided to push the feature out to Snow Leopard users as well. The new native TRIM support does appear to limited to stock Apple drives, as users who have installed third-party SSDs into their machines have reported that TRIM is not enabled by the update.
Mac OS X 10.6.8 also appears to have brought graphics improvements that have been most apparent to gamers. According to one set of benchmarks, Mac OS X 10.6.8 outperforms Mac OS X 10.6.7 in many measure of graphics performance, sometimes by a significant margin.
User reports in the MacRumors forums and the Steam forums similarly point to significant improvements in graphics performance under real-world conditions. A number of users has actually reported significant declines in graphics performance with Mac OS X 10.6.7, so improvements with the new Mac OS X 10.6.8 are certainly to be welcome.
Update: To clarify Apple's TRIM support, the new MacBook Pros released in February shipped with a special build of Mac OS X 10.6.6 that included TRIM support for Apple SSDs. But that TRIM support had not been extended to all SSD-configurable Macs until the release of Mac OS X 10.6.8 last week.
Update 2: A number of users of pre-"Late 2010" MacBook Air models have reported that Mac OS X 10.6.8 does not enable TRIM on their machines.