Currently "Advanced Reports" got the limitation of one single base currency. If your store have multiple currencies (very common in Europe), then it won't work at all. I think there are many many stores that can't use the Advanced Reports today due to this limitation. And it is really sad because it is a great tool and improves the overall impression of Magento.
So, I have built a small extension that takes care of this problem,
(open source, feel free to use this code, I donate it to the community).
It allows the store owner to configure exchange rates to the base currency and then recalculates the data into a single currency before the CSV files are exported.
The extension does not handle historical exchange rates (even if it would be quite easy to add such support). However most businesses in Europe only update the exchange rates monthly in their books so this limitation is for most store owners acceptable.