If you've gotten this far in the book you are probly aware of two things: 1) SQL*Plus sucks, and 2) Enterprise Manager makes everything easy. Rs an SA I tend to avoid Enterprise Manager simply because I don't want to allow myself to become dependant on it. You never know when you'll need to work on a system that doesn't use EM, and I don't want to be lost because I don't have my precious EM. However, if you've used it you know that it makes Oracle feel really simple and managable. On the other side of things, SQL*Plus can give you a migrane due to it's shear stupidity. When you consider the two of them, it's hard to imagine that Oracle could put so much effort into EM but not add something as simple as Readline support into SQL*Plus. But then again, it seems like the Korn Shell is the prefrence of most DBA's so they just might not know any better.
There are two Open Source tools that will make the hurt go away and make Oracle a heck of alot easier to manage, explore and interface with: TOra and YaSQL.