From the "how fast can you go?" files:

Google Chrome who??? Apple is upping the ante in the race for the fastest JavaScript engine with its new SquirrelFish Extreme engine. The new engine according to specs published by Apple WebKit developers show at least 2x faster than SquirrelFish (which already was lighting fast). The new SquirrelFish Extreme will compete in the new world order for JavaScript speed against Google's V8 and Mozilla's TraceMonkey.

Apple developer Maciej Stachowiak blogged that:

SquirrelFish Extreme uses more advanced techniques, including fast native code generation, to deliver even more JavaScript performance....SquirrelFish Extreme uses four different technologies to deliver much better performance than the original SquirrelFish: bytecode optimizations, polymorphic inline caching, a lightweight "context threaded" JIT compiler, and a new regular expression engine that uses our JIT infrastructure.

From where I sit, the SquirrelFish Extreme approach sounds different than what either Google or Mozilla are doing - though perhaps they can be complementary (moreso for Google). Bottom line is a massive spead increase that will make WebKit (and Safari) particularly fast and that means a faster iPhone too (which uses Safari).

It's a marvelous thing to see such a race for the fastest JavaScript engine, it's something that has been a long time coming. I'm not entirely certain that JavaScript is to blame for every browser's speed issues - but no doubt faster engines are a good thing for all.