I just got my visa from the Chicago consulate as well. The Post Office will take debit cards, as well as cash, which was a real time saver for them.

In terms of lessions learned, make sure that you fill in all of the fields on the online form, even if they say optional. My wife did not fill in the address in Brazil (listed as optional on the application), but they wanted it when I went into turn in the visas.

Also, beware, the Chicago consulate is saying it will take 15 Business Days to process the visa. I got mine in about a week (after pleading with them for speed as I am leaving before the 15 business days), but they generally will not expediate it.

Lastly, don't go on a Monday or Friday. The visa clerk warned me the lines are 2-3x longer on those days..