The DragonFly has such fine feature as swapcache with utilization of SSD drive as a cache for HAMMER filesystem metadata/data. I use it in production to boost performance of PostgreSql databases which started to fly after applying a swapcache. The HAMMER itself looks as a fast, power-fault resistant which makes the DragonFly very strong in data serving aspect. For desktop/laptop, IMHO, it's not so good as for servers, all the X/apps stack looks very similar to what FreeBSD has.
Very fast, very responsive, no worries about fsck on boot with immediate recovery. Works great for servers, VMs, NAS, laptops, and desktops. Uses the same packaging system as FreeBSD so you have over 20,000 packages available for easy install. Best of all, the community. Small, tightly knit, really intelligent developers. If you ever have a problem, you can bring it up to them, and the odds are that if they're not overly busy or it's critical that it'll get a fix in within a day or two.
Very probably the fastest Unix available. Developers really take "KISS" seriously and the pace of development is nicely paced. Once HAMMER2 is available and ready for prime time, this will be the OS to take cloud computing to the next level.