Tonearm - 9:05 pm on Dec 4, 2012 (gmt 0)
One advantage to calculating ROI externally is the calculation becomes more precise because it can be recalculated after the order has shipped to use the real shipping cost, it can be recalculated again if a customer returns something, etc. I think Google's requires you to know the final numbers on the order receipt page?
You mention freeing up time, but my external system requires no user intervention whatsoever. I actually don't use the AdWords reports or A/B tests at all. I know that's not the conventional way of running AdWords, and I surely miss out on $$$ because of it, but automation is a priority for me.
Does handing the keys to Google with the Conversion Optimizer really work out?