Re: IE8 / XP
"When you say real-world, what you actually mean is for public web sites. If you RTFRN, that's not what jQuery 2 is intended for as yet. It's largely for apps and other controlled environments."
If only older versions of IE were restricted to such environments but I'm currently working for a client that requires support for IE8 and even DUN speeds on a new public site. It's not just corporate environments that lag behind on technology; there are some groups of the general public that by-and-large don't upgrade unless they have a very compelling reason.