Chris Leary, a Mozilla engineer, writes about JavaScript engines, JIT compilers, Python performance, and programming languages.
HN commenters recommend the blog and link its posts on ARM chars being unsigned by default and on SpiderMonkey.
Good candidate for most evil use of the assumption that char is signed. Incidentally, that's not going to be true on arm[0].
[0]: http://blog.cdleary.com/2012/11/arm-chars-are-unsigned-by-default/
I also did a write up on this called "Mapping the monkeysphere" that you may find helpful: http://blog.cdleary.com/2011/06/mapping-the-monkeysphere/
I can highly recommend http://blog.cdleary.com/