A bit of a flame war going on in the ECMAScript working group (which spices up an otherwise reasonably boring mailing list).
The battlelines are pretty clearly drawn, with Microsoft and Yahoo on one side, and the Mozilla team, Opera, Adobe (interesting, eh? "Enemy of my Enemy" anyone?), and oh, pretty much everybody else on the other side. Or, as you might first opine from that cast, Evil v. Good.
MS and Yahoo think the language is changing too much, whilst the others think that it needs to in order to be competitive for the larger scale programming projects the web is increasingly requiring.
My opinion? As is usually the case, they're both right - you only have to look at the Flash community's response to ActionScript 3 .
In short: They like it - a lot, but its very different than AS2 development.
And, oh, from an implementor's perspective, AVM1 and AVM2 (which, roughly, correspond to ES3/AS2 and ES4/AS3) are two completely different VMs. Is it possible to make one that does both? Sure... but there's no denying ES4 requires *substantially* more effort and complexity to implement (note I'm *not* making an argument about code size here....)
An so, in a deliciously Shakespearean turn, Doug Crockford
That doesn't, however, make it wrong to push in that direction.
And so, lightweight stuff really is harder, but its also a lot easier to write stuff well...