Okay. iPad 2 with iOS 6.
Step 1. Power up Zoom H2 (I used the power adapter).
Step 2. Press "Menu" on H2, scroll to USB, select Audio I/F, select Connect
Step 3. Plug USB cable into iPad camera connection USB adapter, then into H2.
Step 4. iPad says "Cannot use device . . ."
Step 5. Ignore.
Step 6. Choose your favorite audio app (e.g. Garageband, Pocket WavePad, Pure Audio Pro, etc.)
Step 7. Record.
Sounds good. Strong signal. Can select gain (high, medium, low) on H2 for optimal signal. Low noise. Uncomplicated setup. Probably will work with H2 on batteries, too. Key is to power up H2 and configure it as Audio I/F (stereo microphone) BEFORE connecting to iPad USB. Otherwise, I'm guessing the H2 will try to draw iPad power.
Hmmm. What am I missing? Can I really safely ignore the "Cannot use device . . ." warning?
Next episode. Powered USB hub. (Others have indicated this works great)
Coming soon. iMic USB audio interface with XLR microphone (attached with XLR to stereo mini TRS adapter). What fun!