The past few days I've been bringing in my new WIFI-only iPad and trying to use it tethered to my iPhone 5. It's been a frustrating experience so far. I've found that it works OK when the iPad is first tethered to the iPhone, but shortly thereafter the internet connection seems to drop out on the iPad, even though the iPhone is still reporting it to be connected OK.
Using my phone as desktop
I am experimenting at the moment with using my phone as my primary computing device. I think that this is the future. There are phones coming out (hello iPhone 5s) with remarkably powerful processors. We can connect our phones to a bluetooth keyboard at the moment. The next step is to be able to send the display through to a nearby screen.
The good news is that there should be an exponential increase in the need for iOS and Android programmers.