Regarding the look of a BOB, walking around with a backpack in the financial district of San Francisco (or any other Cali downtown) would not look strange at all. I used to work at a law firm where a few partners used backpacks instead of brief cases. Employees who rode motorcycles were typically using backpacks. Many of the wealthiest clients would show up to business meetings looking like the just finished milking cows. I'm sure there are quite a few other cities in America with cultures like that. We aren't in the 70's anymore.

Realistically, I can't imagine myself working in a stuffy city and walking with a complete BOB. I don't work downtown anymore. However, if I did, I would carry only the bare essentials in a rolling briefcase that also carried my laptop and other business stuff. I would go with a backpack for everything if that were most comfortable.