Not This August by CM Kornbluth

After reading Paul's article about the Sci-Fi store by Singularity and Co. I decided to check out a few of the books he had mentioned in the article. While checking out one of them, Not This August, by C.M. Kornbluth on Wikipedia, I found a link to the e-book hosted in the public domain on Project Gutenberg's Canada portal: here. I downloaded the epub version and started reading it on my phone. I was instantly hooked! Its a highly addictive book that I can't recommend enough. Its about USSR and China taking over the USA and in fact most of the world at large in the 1960's. I'm currently about halfway through Book One. Anyone else read it yet? How did you find it?