After two years of cogitation on Scala, the print version of the book is ready! (The Kindle version might take another month or two...).
You can find it here, including a sample of the first 100 pages so you can be sure you like it before buying.
The book is unique because we don't assume any Java background. We went further than that and decided to even make it accessible to someone without any programming background at all (assuming that person is dedicated -- this isn't a "dummies" book; we were shooting more for K&R C, an admittedly lofty goal).
We also decided to make the chapters as small as possible, to make the process into very small steps and to give you the satisfaction of finishing a chapter in a very short time. Because each chapter tries to cover only a single short topic, they are, in effect, indivisible. Thus we call them "atoms" instead of "chapters," and that's where the name came from (along with the mid-century atomic-age artwork on the cover).