UFS remains the default file-system choice in FreeBSD 9.0 and those based upon FreeBSD like PC-BSD and Debian GNU/kFreeBSD, however, the ZFS file-system can be selected at install-time.
Found in the FreeBSD 9.0 kernel is ZFS v28, which adds features like RAID-Z3 (triple parity), de-duplication support, better recovery support, snapshot-level diffs, and zpool split support, among other features (details in this developer's blog post).
For those wondering how UFS compares to ZFS with the FreeBSD 9.0 kernel, I've run some disk benchmarks this weekend using PC-BSD 9.0 RC2 while finishing up the 3.6-Arendal validation, so just sharing these quick results for those interested.
The PC-BSD 9.0 installation was done in its stock configuration for each file-system with the only difference between installs is changing the root file-system from UFS to ZFS. The system being used for testing was build around an AMD Fusion A8-3850 "Llano" APU with an OCZ Vertex 2 SSD.
Those interested in the UFS vs. ZFS FreeBSD/PC-BSD 9.0 benchmarks can find them in full on OpenBenchmarking.org.
There's also some other AMD Fusion FreeBSD 9.0 benchmarks for those interested in the non-disk performance. However, due to the lack of any AMD Catalyst driver port to FreeBSD and the latest open-source Radeon graphics stack not being ported to FreeBSD current either, it doesn't make too much sense to use an AMD Fusion setup in a production capacity under any BSD. With AMD Fusion on FreeBSD you are just left with the VESA driver and the Mesa classic software rasterizer.
Other recent Phoronix tests under FreeBSD 9.0 include a look at the Intel Sandy Bridge performance and Debian GNU/kFreeBSD benchmarks with the 9.0 development kernel.