My experience:
If youre gonna run bolt on hubs it'll not be an issue, one's ok. As far as q/r hubs, be safe, run two. The reason being that in my experience with both singlespeed and geared, even with the knurled/toothed facings (like on Shimano hubs), when I jumped on the brakes for a trial emergency stop, the wheel often slides forward and to the right, due to the amount of forward/torsional force from the brake. Besides, if you run two of Surly's models, you can open bottles whichever way your bike's laying down! *just remember to keep knuckles away from the rotor vanes or use caution if your brakes are hot-makes a funny looking tattoo/scar.
