Apple Tablet May Launch In September

What is the Apple tablet actually supposed to do?
The latest
rumors from Gizmodo point to it essentially being an external monitor you could take with you. Presumably it would have some kind of dock, turning the 10-inch "giant iPod touch" into a palette monitor that becomes a portable media device when separated.
Other indications are that Apple is quietly striking deals with booksellers/textbook publishers for an "educational" version of the tablet, which would presumably target college students and serve as an e-reader.