If you've not already seen it, Microsoft have released a report performed by their JScript (JScript is the Microsoft implementation of JavaScript) team highlighting compatibility with ECMAScript revision 3 with the current browsers. The IEBlog has a good quote about this report:
we here on the IE team certainly believe that thoughtful evolution is the right way to go; as I've frequently spoken about publicly, compatibility with the current web ecosystem - not "breaking the Web" - is something we take very seriously. In our opinion, a revolution in ECMAScript would be best done with an entirely new language, so we could continue supporting existing users as well as freeing the new language from constraints (including the constraint of performantly supporting scripts written in the old language).
A quote like that sure is hard to respond to. Firstly I'd like to point out that "performantly" is not a word - even Microsoft Word agrees it's not so I guess the IE team have taken it upon themselves to "evolve" the English language too without breaking the existing language. Joking aside, their view is to start again from scratch and to make the language something better, but better from their point of view of course. I totally disagree with this approach - evolution is the right way forward as it is with going from XHTML 1.1 to XHTML 2.0, or CSS 2 to CSS 3. Things do get deprecated and changed along the way, and developers and designers have to do their best to allow for people using browsers that don't play nice with the newer standards - but take up of updated standards does happen gradually and eventually the browsers using the older standards can be ignored.
From reading the report you also get the impression that Microsoft are trying to twist their findings in their favour showing where they've kept to the standard they tell you, and where they haven't they say they've done what's sensible and that the standard is wrong.
