X.Org Server 1.8.1 boasts a variety of fixes and minor improvements while all major work is already focused on delivering X Server 1.9 that should make its debut in August.
X.Org Server 1.8 introduced support for xorg.conf.d, marked the removal of HAL support in favor of OS-specific input libraries (such as libudev on Linux), and various other bug-fixes and improvements.
X.Org Server 1.8.1 final isn't very different from the last RC that made the RECORD extension work and received a slightly different SHA1 implementation. There are just two new patches atop X.Org Server 1.8.1 RC2.
In total X Server 1.8.1 provides a couple dozen patches over X Server 1.8.0, which is listed in this mailing list message.