Scott,
I use a Motorola Xoom tablet for remote control of my Canon cameras. There are quite a few apps that are available and I have tried the helicon app, his app will be very expensive and does not work any better than a lot of the other apps out there. Do a search on the marketplace of "google play" as it is now known. For my Canon cameras I use DSLR controller, it works very well. Really nice to see the live view on a full screen tablet and be able to focus and also do focus steps as well as hdr and exposure control, timelapse and just about anything else. The Motorola and just about any android phone will need a usb host cable, which is not very expensive, you can pick them up for under $5 on ebay, then just use your normal usb camera cable. In a quick search I found several that say they support Nikon cameras.
Hope this helps.
Alan