Oh boy, just what we need. Drama between open hardware vendors. Neither of these responses feels like the complete story to me. I hope there's a path forward to heal this rift in one way or another. Both SparkFun and Adafruit are doing amazing things for the community and I would love to see both continue to thrive.
Seems to be the inevitable trend... Just in recent times: Pebble drama, Arduino joining the dark side, now Sparkfun & Adafruit. End of an era
Note that Sparkfun has been less and less of an "open hardware" vendor, as they've dropped the open aspect on some of their most popular projects.