Currently, courses are offered for free, but Coursera ultimately intends to generate revenue. To that end, they've begun implementing some pay services; for example, they recently introduced a special service called Signature Track that (for a premium) awards students who complete courses with certificates securely tied to their identities, making it easier to share them with potential employers, etc. It may be their hope that revenue from these ancillary services will enable them to continue providing the course material for free, but I suppose some sort of fee-based system isn't necessarily out of the question in the future. All of which is to say: I'd recommend availing yourself of the service as soon as possible.
As with a "real" course, the material is broken up into units (normally weekly, in my experience), so you and your virtual classmates progress through the units together; course-specific online forums facilitate communication between students and teachers. Lectures are delivered via online videos with short questions embedded throughout to gauge your understanding; you can listen to the lectures at your own pace (within the time frame for each unit, of course). Quizzes at the end of each unit generally comprise part of your course grade, which may also include graded exercises, projects, and exams.
Given Coursera's format, it should come as no surprise that a large number of technology- and programming-oriented courses are offered. While there are no courses (that I'm aware of) for learning Java, I would recommend the Learn to Program: The Fundamentals and Learn to Program: Crafting Quality Code courses offered by the University of Toronto. As their names imply, they're intended to provide an introduction to programming concepts in general, but Python is the language of choice so they end up being pretty good introductions to Python specifically, too (Python is the primary scripting language used by Sikuli, the UI automation tool I've discussed in other posts).
If you're hesitant to jump into the pool and would like to sample a course to see if this learning method is right for you, there are currently two computer science courses available for self study: Introduction to Databases and Computer Science 101, both from Stanford University. Without due dates and a live online forum (and there's no statement of accomplishment for completing self study courses) it's not quite the same thing, but at the very least you can get a sense of what online lectures and quizzes are like. The Computer Science 101 course may seem very basic to people who work with computers on a daily basis, but for anybody unfamiliar with programming/scripting, the first three units teach some fundamental concepts including variables, dot notation, and flow control, albeit via a simplified proprietary Javascript-like language developed by the course instructor (Nick Parlante-- who also developed Google's Python Class). The "image puzzles" in the course are also kind of cool.
