Progress!  80 Zombies dipped and drying after a quick bath in Army Painter Quick Shade Dark Tone.

They are pretty glossy right now, but I can fix that.
Overall I'm fairly pleased with the dip.  You can quickly and fairly easily shade hoards of zombies (took about an hour to do 80 zombies) with fairly minimal effort.

 It makes a hell of a mess though.  If you end up trying this I highly recommend wearing latex gloves, spreading copious amounts of news paper and having paint thinner on hand.  I accidentally dropped a total of 4 models into this dark viscous goo....