Question: I know a fair amount about the current javascript engines. What techniques have arisen in the intervening time? Please provide links to freely available information.

edit:

To clarify, I'm looking for new techniques that are being implemented or have recently been thought up for improving javascript execution speed.

Answer: 
Here are some references that came from the top of my head:

* [V8](http://code.google.com/apis/v8/intro.html)
* [Webkit](http://trac.webkit.org/wiki)
* [Spidermonkey](http://www.mozilla.org/js/spidermonkey/)
* [Gecko](https://wiki.mozilla.org/Gecko%3aHome_Page)
* [accelerated compositing in Chrome](http://www.chromium.org/developers/design-documents/gpu-accelerated-compositing-in-chrome)
* [Native Client](http://code.google.com/p/nativeclient/)
* [WebGL](http://en.wikipedia.org/wiki/WebGL)
* [installable web apps](http://code.google.com/chrome/apps/)
* [crankshaft](http://blog.chromium.org/2010/12/new-crankshaft-for-v8.html)

Please notice that at this moment (in the modern browsers) javascript isn't the bottleneck anymore in execution speed of the page. now that that problem is solved a lot of the browser manufacturers are focusing more on other aspects in the process of bringing a page from the server to the user. For instance a lot of the graphically rich pages that are standard now would benefit from the power of modern GPU's. It is often overlooked but rendering a typical page now takes generally more time than executing its scripts.
General details can be found at wikipedia.org and more detail at the Sun microsystems website and its links to associated sites. Some techniques now in use with recent versions of IE and Firefox and other browsers are forms of dualprocess or multiprocess operating in their own control structure to enhance performance specifically and for improving the general browsing experience. The use of javascript is decreasing in some nations and increasing in others as the relevant public internet server population changes over time. Only when the javascript parsing and interpreting code is rewritten in a faster language or some form of multiprocess is introduced to code on the servers or operating in the user's computer will the speed increase.