Microsoft's JScript team, keenly aware that they are part of the problem, write:
To make it possible to achieve such implementation conformance, the first step is knowing where the divergences are. We in the JScript team are looking into where various browser based implementations diverge, where our engine is incorrect in its interpretation of the specification, what if any de facto compatibility conventions have been reached, and the value of codifying such conventions into the standard. We’ve published the first draft of JScript Deviations from ES3 as a starting point.
This is the most beautiful ugly document I've ever seen.
Kvetching aside, seeing a document like this come from MS is a dream come true. Now they can continue this excellent trend by... releasing fixes for all of these problems in SP3 for XP and SP1 for Vista!