I came across a neat product called CamRanger (
http://www.camranger.com) that connects to your camera with the normal USB connection and then creates a WiFi hotspot of its own. Your iPad (or laptop) can then log onto the wifi hotspot and get the live view, capture images, do focus stacking, do time lapse, HDR bracketing etc. It is sold from their site at $299 and I was sorely tempted (just because it was really well constructed and I was impressed by the knowledge of the inventor/CEO when he demo'd it to me.)
If anyone has one, let me know what you think!
Steve