I think qemu works better for bsds you might try that
i'm anxious to see hammer stabilize and get ported to other operating systems.
I've given a quick shot to the previous release.
Hammer seems stable, after some days of moderate use. It has nice features too, but it requires a "pruner/reblocker" cron job once in a while that might impact performance on a busy machine.
I'm more curious as to how the latest release scales to multiple processors, given the additional MPSAFE advances they made.