I currently have an example of how to use Yahoo! Pipes in Chapter 4 of my book. Pipes continues to advance quickly beyond the point I last took a close look. At the start of its life, Pipes dealt only with acepting inputs and creating outputs that are RSS or Atom feeds. Now, it seems to be able handle a broader range of inputs: XML documents in general (I think) but also JSON. When I last looked, the output is still primarily feeds -- though KML is now one of the outputs of Pipes, allowing for the generation of mapping data that can be plotted directly on Google Earth and Google Maps. I'm looking forward to being able to produce a broader range of outputs as well as being able to plug in third party filters and transforms.

For an engaging talk on the subject by the creator of Pipes, see it on Google Video.