Alfred: I've fixed the mycontroller typo. The second script may yield a "TclError: wrong # args" error if you click on the canvas, but the posted version seems to work as expected if you drag lines.

Stewart: In my experience, being able to focus on one problem at a time is a great way to reduce the complexity, not increase it. As for other advantages, I hope to be able to address them in a followup article (feel free to look at the WCK version of this article for some hints).