I have been doing a bunch of testing with the new 8GB Eye-Fi card.
You have two options really, because you can not format the card into two partitions and get Eye-Fi to work from the second partition.
First option is to format FAT 32 then copy CHDK onto the card and just using the firmware update method boot CHDK manually.
The second option, which is the one I settled on, is to partition the card to two 4GB partitions, format the first partition as FAT 16 and then load CHDK onto that partition (as well as the Eye-Fi stuff). The second partition is more or less a waste since the camera or CHDK can not access that partition. (If you switch to the second partition using CHDK it will give you an Card Error message)
The benefit to me over the standard 4GB Eye-Fi card was the ability to do Ad-Hoc transfers and handling of RAW data transfers.
You could also buy their older 4GB Pro card and do the same thing, but the older card has to be filed to give the card the ability to fool the camera it has a write protect lock switch.
Furthermore I found that everyone sells the old card for about the same price as the new 8GB card. So whats the difference. The new 8GB card already has the write protect switch. So you can forget the filing of the card.
I guess no matter how you look at it, there is no way to actually use the full 8GB of the card. I faced that reality and moved on just happy I can handle the RAW and Ad-Hoc transfers.