Following your tutorial, I put my first app together in not much longer than it took to read the tutorial. Then I started fiddling, and broke it. I couldn't figure out how to back out of my changes, so I just trashed my work and built it again. Now, no doubt, I'll break it a different way.
So I think O'Reilly needs to appeal to all levels of readers -- absolute beginners included. I actually have a target function for a browser app, and the functionality hinted at for part II is needed for it. But I'm not afraid to make mistakes in the meantime, especially when it's so easy to rebuild the app from scratch.
However, I hope in a separate article O'Reilly will address "backing out" of mistakes. I've tried using CVS for some of the websites I've built, but never really figured it out. I gather SCM is something similar (or not, I'm probably wrong). I would love to know how to go back to a previous build of my app to erase the screwup I just performed. At my level of experience error messages are impenetrable: I'd rather just go back a step and try something different.
In the meantime, I'm going to go back to my app and see if I can figure out how to set up a page-load progress indicator. Thanks!