Interesting that they decided not to do a responsive design. Instead, it serves up different HTML if you send a phone user-agent. I've been trying to decide if this is a good idea for my own project.
Our desktop site is pretty large. Check the graph in the blog post- the mobile pages are about 1/10th the size of the desktop CSS and JavaScript. By avoiding a responsive design, we can make things load disproportionately faster for our use case. On top of that, it's isolated so we're less likely to break views by adding features later. Pretty fun.
We tend to avoid user preferences. If it ends up being a problem, we'll lower the text size at some point.
I can't resist doing code reviews even when I'm away from keyboard :)
I like word wrap too, but I'd like to be able to switch it off. In my desktop code editors, I generally use proportional fonts and enable word wrap, but sometimes I also like to be able to see the structure of the code without the word wrap.
I think font size and word wrap should be things that are easy to toggle right there while you're looking at the code. Not in an option setting somewhere. Or enable pinch-zoom for the font size and just have an option to toggle word wrap.
I'd love to know the technical approach on this. That is, is the different HTML/CSS/JS view called by the Rails controller, based on the request's user agent? Though responsive designs are often a good call, I completely agree with your decision to do custom views here. I'd love to know where in the process the filtering happens, though, such that you retain the URLs (no "m.github.com") and yet have the customized view. Any backstory on the technical aspects that you can share?
http://37signals.com/svn/posts/3257-backstage-basecamp-for-m...
https://public.basecamp.com/1679267/projects/764604-bcx-phon...
Responsive feels great with huge/big/medium displays. With tiny ones I would go with a specific layout (like github did).