As of last week, using the Servibanca ATM in Cali I received the exchange rate of 2,783.58 (This actually will be adjusted up slightly when my bank refunds ATM fees). There was also a $400,000 limit ($143 US) per withdrawal - I did not play around with the number of withdrawals permitted per machine/per card. The exchange rate for cash dollars at the official casas de cambio was either 2,620 or 2,610 depending on which one.
I finally figured out the crazy airport tax - once again I did not pay ANYTHING. Of course, I picked up the exemption upon arriving. The explanation of no fee by the AA agent was that the other portion of the tax is now included in your air ticket price - mystery solved. Maybe that differs with other airlines?