I use a Nikon D3, iPad2, Eye-Fi x2, Zalip wireless router, and ShutterSnitch. Tethering work but there are some issues.
The biggest issues is that the wireless signal from Eye-Fi cards is super weak. By the time I put it in a CF adapter (with metal casing removed to help signal) inside a pro magnesium bodied camera, the signal is next to nothing. When I did my initial testing with my ipad and router on the desk and my camera in my hand, my transfers would stop when I held the camera normally and resume when I removed my hand from the grip so I was no longer covering the card.
To get around this, I have to wear my router hanging around my neck so that it's about 12" away from the camera. When I do that, I can shoot all day long and the iPad can be in the other room and still connect to the router. The weak link is the Eye-Fi card so as long as the router is close to the camera, I'm good.
Eye-Fi has come out with their direct-mode and a mobile app. I haven't tested this but I don't think it would work at all in my case because I would be removing the router and there is no way the Eye-Fi would reach directly to the iPad. Keep in mind, you might not have any of these issues if your camera supports SD directly without adapter and has a plastic body that won't block the signal.
Once you get the connection sorted out, ShutterSnitch works great but it does take about 5-7 seconds from the time I click the shutter for it to appear on the iPad. It's not really useful for me if I'm doing a studio setup etc. because it takes to long to see what each change to my lighting is doing etc. but for group / model shots, it's awesome. I love handing the iPad to a mom while I'm shooting pics of her kids and she can see what we're getting. When I'm done, I let models quickly go thru and tag the images from the set that they like.
The Author of ShutterSnitch is really helpful and answers posts on his forum. I made a feature suggestion and he implemented it in the very next release a couple weeks later.
Over all, it's very cool to be able to tether but you have to understand it's limitations.