FreeBSD 9.1 has been months behind schedule, but the FreeBSD 9.1-RELEASE announcement was finally issued yesterday on 30 December.
Key highlights of FreeBSD 9.1 include the Intel GEM/KMS kernel driver that was ported from Linux, the netmap fast user-space packet I/O framework, ZFS improvements from Illumos, the CAM target layer, an optional C++11 stack using LLVM/libc++/libcxxrt, various new hardware drivers, kernel support for the AVX FPU extension, and numerous improvements for IPv6 hardware offloading. The long-awaited Intel KMS support for FreeBSD is quite exciting though it's a constant challenge of back-porting changes from the Linux kernel. There's also no official Radeon or Nouveau driver KMS/DRM drivers in FreeBSD.
The FreeBSD 9.1 release announcement with more details can be found at FreeBSD.org. Earlier this month on Phoronix were FreeBSD 9.1 benchmarks against Linux and other operating systems.