This is a little old, but Matthew Dillon noted the status of his Hammer2 work a little while ago.  Some highlights: he’s intending Hammer2 to be usable on a single host by the time of the next DragonFly release (summer 2014), the Summer of Code project for compression has already been integrated, and he listed different parts of the work that may be interesting for anyone wanting to chip in.

Slightly related: Matt posted some Hammer2 comments on the DragonFly 3.6 release story on Slashdot that may be interesting.  Don’t bother reading the other comments; they’ll make your eyeballs bleed.