Hi,
I wonder if a similar "theme" is apropriate for proposed book. Graphics and sounds give a very direct feedback to the programmer, and I expect that helps with the motivation. Perhaps a single largish application could be the "end product" of the book. Like a game or something. You'd start off with some examples early on, and then as quickly as possible start working on the low level utility functions for the game, moving on to more and more complex things as the book progresses. You'd inevitably have to deal with things like performance and other "real world" tasks. It might be difficult to find something which would work well, though.
Maybe this idea (ok, isJust) comes to mind because I'm looking around at cakephp, which is a rails like framework for PHP, but a real-life example could be something like rails. It need not be as extensive or fully fledged, but enough such that people can get the hang of things and take it from there. That would include DB interaction, web interaction, logging, XML and what have you. It might just require enough of the more exotic Haskell stuff to get newbies up to speed. Details can be tackled either when they arise or deferred to an appendix, if they bloat the actual issues that is being explained. Just my €.02 -- Andy PS. I still belong somewhat to the latter category of the subject.