for the past few years, I have been using netbooks to program the NXT. I would like to move into the 21st century and use ipads. Is there an ipad app for programming the NXT brick?
There are no programming tools available on the currently available iOS devices, including iPads.
Technically speaking, this is because the iPad lacks support for the correct Bluetooth profiles that would allow a direct connection. iPads also have no USB port that can be used in host mode to directly connect the NXT (the USB to dock adapter from the camera kit does not work!).
Theoretically it should be possible if you take part in the Apple Hardware Development Program and write your own driver. But this is possibly out of scope for the rest of us ;-)
A mentioned workaround is to create an application on the iPad for source code editing and use a Proxy-PC that communicates over WiFi with the app, compiles the source code (e.g. NXC) and sends the binary to the NXT. If someone has done this, please let us know!
With the new EV3, things will change as this brick is able to communicate over WiFi. And Lego announced some kind of iPad and Android IDE for EV3.