SFE is using similar tactics to Chrome, but in slightly different ways. They are using bytecode optimization, inline caching and a JIT compiler to gain the speed boost. you can get details from the Surfin' Safari blog.
More important than the tech details is the movement. Sure, they probably started working on some of this before Chrome hit the news but telling us about it now, rather than when they are ready to ship lays down their entry in the browser speed contest.
The guys at Google have also said they will be allowing plugins and scripting similar to Greasemonkey, (is it telling that the original Greasemonkey developer now works at Google.)
Of course I haven't mentioned what MS might be doing with Internet Explorer 8. I've downloaded and attempted to use Beta 2 and it seems to be faster than IE 7 but it is still too unstable to be usable - I tried several times to alter the default search engine but could not get that to work, for example. I'll try again on another machine rather than my Mac under Fusion and see how it goes.