Lots and lots of CSS bugs. So many developer hours have been wasted debugging IE6 issues it's obscene.

Thank you. Now we're getting somewhere.

Try submitting an AJAX get request with a variable than ends with UTF-8 data (chinese glyph) and has been fetched from the DOM.

I hate IE6.

Aren't there libraries that handle that kind of stuff for you?

I got fed up and decided not to make things work anymore with IE, when I realised I had a folder of little tweaks that I was including in everything called 'IE Fixes and Workarounds'