Keeping Moodle Versions Straight
I wrote this book using version 1.9.9, and it covers Moodle versions up to version 2.0 (which was recently released). I have confidence that this book will help you set up courses and teach you all you need to know for versions 1.8 through 2.0.
The main changes in the new release are designed to give third-party developers more flexibility and scalability and to integrate Web 2.0 technology. Moodle 2.0 is still viewed as beta at the time of writing this book, which means the changes are essentially transparent to you as the end user. (Again, though, the material covered in the book is applicable to get you going if want to upgrade to Moodle 2.0.)
Moodle docs, which are referenced throughout the book, are for versions pre-2.0 with notes where upgrades have taken place. Unless you're a developer or actively want to test the software for bugs and intend to contribute to the development of 2.0+, I strongly recommend that you use the latest version, 1.9 (which to date of publication is 1.9.10), because as the Moodle.org site reports, minor upgrades to Moodle 2.0 are found weekly, and patches will be released regularly. Hence why you see versions 2.0; a month later you see 2.1; and then 2.1.1
Moodle has been consistent with every new release, leaving the front page, navigation, and setup pages for teachers and learners the same. For most instructors and teachers, the main difference they will see is changes in how files are handled in the new versions. As with any new releases, there are bugs and minor issues, and the Moodle forums are quite hot with activities around these issues. No doubt all minor issues will be resolved over time.
Please see the Moodle 2.0 release notes at http://docs.moodle.org. Many forum discussions still say there are improvements to be made and changes in the wind. I know I will be sticking with 1.9+ versions for my teaching courses for some time yet, though I'm excited about the future possibilities, especially the potential for integrating third-party modules and mobile apps.