As the sole developer and maintainer of a Javascript library for working with the <canvas> element, most of the problems I encounter when working on the code are to do with things which work fine in every other browser, but die in flames on Safari.

I'm getting to the stage where dropping support of the Safari browser (and thus all iOS browsers) is something I consider on an ever-more serious basis. One of these days I'm gonna add a big banner message to the library's website stating: "If you need your canvas to work on Safari/iOS, try coding it using [list of competing canvas libraries, with links]."