how far can you use it from the camera?
I have used it at up to roughly 200~250 feet away, indoors in a radio and electronics intense environment- more details below.
Did you use it on an iPhone? - that would be the easiest thing for me...
Previously used it with an iPhone 4, since last week I am now using it with a fourth generation iPad as well.
If you happen to use it with a D800; any problems?
I've only used it regularly with Canon EOS 1Ds Mark III and 1D X cameras. The distance test may also have been done with a D800, I'm not sure as this was back in January. The distance test was done indoors at a pro shop /print studio / rental studio facility and I wanted to see how it worked in that environment. The cameras were set up up at the front of the store and I went all the way back to the rear of their largest studio at the back of their building. It was a WiFi rich environment in a metal framed building with at least four walls, a printing/ retouching studio, multiple offices, a lot of flash rental gear, and at least two bathrooms between the iPhone running the CamRanger app and the CamRanger equipped cameras.