X Server 1.6.4 brings seven fixes, which is slightly less than some of the earlier bug-fix releases, but it's an improvement nevertheless and can be used by the distribution vendors that will be shipping with X Server 1.6 in their next round of updates due to the late X Server 1.7. None of the bug-fixes stand out in particular, but the 1.6.4 release announcement can be found on the mailing list along with the source download links.
X Server 1.7 RC3 is the third and final test release for this new X Server that brings Multi-Pointer X, X Input 2.0, VGA Arbitration, and other new features. There are quite a number of bug-fixes in this release candidate compared to RC2. As a small note, X Server 1.7 will actually be the first release in quite a while where there is a usable XQuartz server from an official X.Org release. This release announcement can be read here.
Peter Hutterer expects to release X Server 1.7 final with X.Org 7.5 within the next week pending any changes to the blocker bugs. Cheers (or rather, Prost!) to this hopefully being the last much-delayed X Server release, thanks to the proposed process changes currently being discussed for X.Org Server development.