1. Respond.js is not in the footer, it is inside the <head> tag. See here: https://github.com/thatcoolguy/gridless-boilerplate/blob/mas...
2. HTML5's syntax is not very strict, but I prefer closing void elements because I think it improves readability.
3. I chose not to add any responsive image style by default because of IE problems and Windows' rendering. I'm thinking of adding that soon.
The source formatting kinda threw me off with the entire head being tabbed and the empty body, maybe add a little dummy HTML inside the body like the H5BP?