For those unfamiliar with MidnightBSD, like PC-BSD and GhostBSD, it aims to make FreeBSD easier to use by desktop BSD users. MidnightBSD strives to be an easy-to-use BSD operating system and to include all software needed for traditional day-to-day desktop users.
The MidnightBSD 0.4 release presents a new mport package management tool, has turned into a more rolling-release style distribution with regards to package updates, and pulls from FreeBSD 9.1 with ZFS (ZPOOL 28/dedup), LLVM+Clang, and migration to GPT for the default install method. MidnightBSD 0.4 has also been updated against the new FreeBSD USB stack and CAM-based ATA support. Being based on FreeBSD 9.1, there's also Intel KMS support and other goodies.
More details on MidnightBSD 0.4 can be found at MidnightBSD.org.