Hmm... I didn't say that I'm "not interested in testing at all", and it's unfortunate that I came across that way. In fact, years ago I created a Rails tool for performing a/b split tests:
https://github.com/flyingmachine/rails_ab_split_tester . Also, in the resources section of the site I link to Don't Make Me Think, which strongly advocates quick, cheap user testing. However, I felt like a discussion of testing was outside the scope of site. And unfortunately, I don't have the time to conduct proper tests myself. I wish I did, but I've spent a great deal of time on the site already, and it's time for me to work on other things.
However, this is why I made the site available on github - if you'd like to improve the site, please do create a pull request. If I come across a little surly here, it's because it's bizarre to me have put so much effort into the guide, motivated solely by my love of design and desire to engender it in others, only to read that somehow I'm exhibiting disrespect for great design.
Re: "clean" - keep in mind that the site is meant to be an introduction to design. People who have no design vocabulary nonetheless have an implicit understanding of "clean" and "messy". For many people, "clean" can in fact be a goal, and I felt no need to ignore the way people actually use the word. Also, it made for a fun title :)
I try to explain what I mean by "clean" design in a way that's not limited to personal aesthetic - it's design that allows the audience to quickly find the information they need. Did that not really come across? If it did - do you think that making information easy to find is not a valid goal of design? Or do you disagree with my definition of "clean"?
It seems like we're not using the word "clean" in the same way, but if we are, I'd love to hear your thoughts on why you think "clean" isn't better or necessary.