One can already do this with the Canon software bundled with their DSLRs. Having it available on the iPad, however, is quite novel. Not sure what Nikon has in terms of Software – they probably have something.
OnOne Software has this really cool iPad app called DSLR Camera Remote HD – it looks very useful.
Now all that is needed to make it better is to pair wireless access to the DSLR Camera Remote HD with Okii’s USB Follow Focus then it will be beyond awesome.
Imagine a preview of Live View on the iPad – fullscreen – with overlay controls that you can dial in through the touch interface.
For now you can get this OnOne iPad app for just $50 – pretty much a no brainer if you have an iPad – especially with that Auto bracketing feature.