One of the most interesting improvements made in DragonFly BSD are about the HAMMER filesystem which is now considered ready for productional use. It is also now possible to boot from a HAMMER-only disk, though this is still not recommended. On the kernel side first steps toward AMD64 support have been made, thanks to the Google Summer of Code 2008. For a complete list of changes and release notes have a look at the DragonFly 2.2 release page.
I can't wait to play with a full-featured HAMMER filesystem, that allows multi-master replication! ■