Do you feel this way about all three?

To me, abstract classes are relevant since the user guide is not only about useful code, but also how to begin subclassing for your problem.

But if an abstract class takes a long time to discuss in exchange for a relatively minor convenience, then there's not a lot of loss to the user not knowing about it. I feel this way about the *SingleInputProducer classes, which essentially save the user the trouble of making a KijiDataRequest.

I'm amenable to removing everything except the concrete examples if you recommend it, in a future commit. Can you also look at the BulkImporter section and tell me what you feel about that?