I love them, and use them - both a portable pump organ & an Indian baja - as described by DebC above, but the idea is that you pump the bellows with one hand & play the keyboard with the other, using the various drone stops along the way. See: http://www.youtube.com/watch?v=MnZ9GbWqMrg

Here's some vintage Planxty with Christy playing pedal harmonium: http://www.youtube.com/watch?v=3Z3A5Tgy47M

And not forgetting Ivor Cutler: http://www.youtube.com/watch?v=LddPuhzt0F4