The cynic in me wonders if the inefficiency and inaccuracy that comes with using humans to crunch numbers gives them more room for error. It's pretty hard to pressure a computer to make the numbers work in your favor, but it's pretty easy to push a low level employee to do something unethical.
It might happen, but at least in the segments of the industry I work in, I don't think it is common. What is more common is human error. Most of the businesses I deal with are highly regulated, and they wouldn't risk fudging the numbers. In fact much of our business these days is related to enforcing compliance regulations.
If you knew how dirty most financial data is when it is released, you would probably be checking your statements more carefully.
