According to the release notes of the latest build of Mac OS X 10.6.8 seeded to developers on Friday, the upcoming upgrade will contain improvements for Preview, VPN and IPv6, but more importantly it will make changes to the Mac App Store application in order to get it ready for Lion's digital distribution this summer. As noted by 9to5mac, the installer of build 10K531 reports 10.6.8 will "enhance the Mac App Store to get your Mac ready to upgrade to Mac OS X Lion", as well as "identify and remove known variants of Mac Defender." Last week, Apple indeed updated a support document related to the Mac Defender malware promising that "in the coming days" a Mac OS X software update would be released to automatically find and remove Mac Defender and its known variants. At this point, it appears Apple is getting ready to release Mac OS X 10.6.8 relatively soon, perhaps even ahead of the WWDC that kicks off on June 6.
As for Lion's release, latest rumors indicated that after widespread internal testing Apple could release the OS sooner than initially expected -- not in July or August, maybe at the WWDC. A WWDC release, however, would appear strange considering Lion Developer Preview 3 still has several bugs to fix and a GM build hasn't been seeded yet. Apple is undoubtedly "enhancing" the Mac App Store's underlying code to make the transition to Lion easier and the download process as smooth as possible, though it seems likely that the company will also sell boxed copies (DVDs or portable USB keys, as many suggested) for those users unable to download gigabytes of data from the App Store.