I am running yosemite(10.10) as well and plugging in edison via the small breakout board (from intel) does not work. I have other thumbdrives and the like which are recognized fine, this is the first USB device I have seen not be able to be recognized at all in yosemite.
I have tried both USB ports on the small breakout, the one closer to the edge (J3?) does not appear to do anything, the one closer to the middle (J16?) will power the board, and I can hold the button to power the board on and off. But still, no dice. Very excited to play with the board if I can get it working!
Thanks,
Anthony