Nikon D800 Found to be Incompatible with Eye-Fi Cards for Wireless Transfers
Update: Eye-Fi has released a firmware update that fixes this issue.
If you shoot with a Nikon D800 or D800E and have been experiencing issues with wireless file transfers using Eye-Fi SD cards, it's not just you: Eye-Fi has found that some aspect of the cameras' SD slots make them incompatible with the cards.