I was working on an HTML5 canvas pixel editor at some point. It was rather frustrating dealing with the Retina display, blurred edges, and anti-aliasing. I'm curious if this situation has improved at all.
Yeah, the situation is still pretty grim. I spent a good half week trying to get canvases scaling while maintaining chunky pixels across multiple browsers and finally gave up. In Goya, all of the pixels are drawn as rects. I actually read your 'drawing pixels is hard' article two or three times while I was trying to track down a good solution.
Sorry my comment was not clear - I'm not the author of the linked article, but it's a good primer on the issue (even though I believe some of the solutions are out of date).
I also rendered pixels using rectangles and lines using my own routines. If I recall correctly, the editor worked fine when zoomed in 4x-8x. The problem was rendering the image 1:1 or 2:1. The rendered image looked a bit blurry compared to Graphics Gale and grafx2 (the two pixel editors I was using for inspiration).
See here for more info: http://phoboslab.org/log/2012/09/drawing-pixels-is-hard