A guy I know has a Eye-Fi card for his 20D and he has been getting some pretty poor results from his. As he shot basketball T&Is, I watched his setup in action and here is what I gathered:
He was shooting a 20D with Eye-Fi card, had a D-Link router (not sure what its specs were, but it was small without external antennas), was running Picasa 2 on his laptop, and had a monitor for customers. There was about 6' between the camera and the router, and 6' between router and laptop. I don't know if the router was physically connected to the laptop. When he would shoot a picture, the file would not appear on the laptop for up to 10 seconds. He and his wife both said that connectivity is spontaneous, that you may get an immediate transfer sometimes, while other times you may wait for a minute or longer before they transfer. His theory was that because the card was in a SD to CF adapter, and because of all the metal in the camera body, he couldn't get connected very well.
