When it comes time to purchase, every once in a while the same person that downloaded comes to our online purchase page and we're able to attribute the sale back to the channel/ad/blog it came from.
Most of the time though, someone else (the boss, a purchasing person, etc) on a different PC comes to our online order page and pays. From Analytics point of view they came from nowhere. Or worse, they fax/email a purchase order.
I would love a way to accurately track the source of our sales without introducing painful process (requiring some sort of download ID for example) to the purchase process.