I am glad that you brought this up... I agree that the tank bag does take away from the lines of the bike but a backpack is sumbersome as well. There is such little room under the seat on the SS, so I have been looking at the SW-Motech bags like this one:
SW-MOTECH QUICK-LOCK EVO Engage Non-Electric Tank Bag | 7 Liter | TwistedThrottle.com
SW-MOTECH QUICK-LOCK EVO Engage Non-Electric Tank Bag | 7 Liter | TwistedThrottle.com