I just went through the process in Vancouver.
My american visa expired late july and applied for a renewal before that date. After paying the fee they scheduled me for an interview august 5 (completed the online application form and payment on June 23).
They recommend to show proof of income if you are working, offer of employment, why do you want to travel to the states.
I got to the consulate, submitted my passport, waited for like 45 min until my number came up for the interview which didn't last more than 5 minutes. pretty straight forward questions.. what do I do? how long i've been in canada? do i have relatives here and why do I want to go to the states.. I said that I wanted to renew my visa because might be going back home in december and ill be staying in houston, tx for a couple of days.
Right after that he told me that my visa was approved, he kept my passport and gave me a piece of paper with info of how and when to pick it up. 2 days ago I got a phone call saying my passport and visa are ready for pick up.
They didn't ask for my work permit, job offer letter, bank statements, nothing... THIS DOES NOT MEAN THAT IS ALWAYS LIKE THIS. I guess if they are not very convinced then they will ask you for some documents.
Oh and one more thing. Don't bring a cellphone, usb keys, headphones.. any electronic equipment or even keys with pocket knifes. Its obvious that they don't let you in with them but they don't keep them for you either. I had to go to a restaurant next door and pay $10 bucks (oh yea they charge) for them to keep your stuff while you are in the consulate. When I went to the Canadian Embassy back home, they keep your phone, keys, etc at the entrance..
anyways..good luck and hope this helps