I have adapted my RF73/RFM73 library for the NRF24L01. These chips are almost identical, except that the RFM73 has a second bank of registers that must be initialized with some magical values. The RFM73 has a special command to switch between the banks, and a bit in the status register that indicates the current bank. This provides a good mechanism to test for the presence of the chip (switch the the other bank and check that the bit in the status register toggles), without disturbing any settings or transmitting anything.
Has anyone found a feature of the NRF24L01 that can be used in a similar way to test for the presence of this chip?