I'd love some more details: 1. How did you come up with this as a topic for an eBook? 2. Is this your area of expertise, or did you see a niche market? 3. What are some specifics on your AdWords campaign? 4. Looks like you have a strong online presence. Do you think that helped sell your book or was it completely irrelevant to its success?
2. No, it all started w/ a passion for languages. I had the idea to write a book after reading 4 Hour Work Week
3. What do you want to know exactly? I used the keywords "create programming language" iirc
4. Yes, I think it helped a lot. The only "marketing" I've done is on Twitter and my blog (also recently on my site http://refactormycode.com). I was surprised by the success, but I'm now convinced that OSS can pay in a way or another.