Loved it. I'd like to see a PDF version. I see that you mentioned in an earlier post that you're not that familiar with generating PDF files. I'm not that familiar, either, but from what I've gathered most authors use TeX markup with their writing and then use the TeX source to generate PDFs via pdfTeX.
Anyways, enjoyed the writing and the pictures. Great job on the formatting, too. Really liked the "don't drink too much kool-aid" segments. I did find some of the code samples a little confusing, but I'm, admittedly, an amateur programmer and I've never dealt with Erlang before. I didn't really grasp what an Erlang module is or the specifics of using spawn. I gather that these are probably basics that you may expect a reader to already be familiar with, maybe covered in an earlier chapter, but maybe you could add a sentence here and there explaining the code samples a little more in depth.
I did assume previous knowledge for this chapter, but everything you need has been shown in the ~10 previous chapters. So far, the book is still meant to be read in a linear manner, but this could change once enough material is covered. I could add a few more links in a wiki-like manner.
Thanks for the positive comments, too. Much appreciated.