So after a little confusion (reading the rev B instructions with the rev C board), I've got my power board under construction.
Soldered my power connections (12 gauge wire to the middle, and have soldered deans sockets all around. Took great care that all my Deans connectors had the correct polarity.
But... When I test the power connections with my trusty ohmmeter, two of my negative connections are not connected to the other two. If you look at the bottom of the board, there's a central trace (+ve) which connects all four ESC Deans sockets to the positive. There are two smaller traces each of which connects two of the negative connectors. One of these traces has the negative power line going in to it. The other has nothing (top trace in this picture)
There seems to be space for a jumper between these negative traces (on the top of the board) but I didn't think the rev c board needed a jumper. Have I just missed something obvious?
check the top side...
and look here: http://code.google.com/p/arducopter/wiki/Quad_Soldering_PDistro_RevC
I purchased a REV C or REV D power board (cant remember which) as part of a standard Arducopter kit (frame only, no processor or IMU) in November 2010, but the power board was more recent (and different from) the one in the illustrated instructions. It has 2 small jumper wires presoldered to it in opposite corners. I suspect these are missing from your board.