I got this tip off of a CNet how-to....
If you have the camera connection kit...
Insert the part that has the USB connector on the other end (from the 30pin side).
Then, if you have a microphone...like I have one by Logitech...then you can insert the USB end of the Microphone into the USB connector on the kit piece, and it works!
Now, just use an app that uses the iPad mic and it will pick up the mic into over the USB mic.
I use the Glee app. Until this, using the Glee app with the iPad was a pain because the mic is on the backside. Now, you can put the mic wherever you want it. That is cool.
Apparently, some USB keyboard work too, as long as they can take power from the iPad (2012 version in my case). This works with the Logitech Micro an you can see the green led light up on the mic when you turn it on.