Whatever some benchmarks (probably involving handing control off to C or C++ as quickly as possible, like any interpreted language benchmark aiming to demonstrate its "blazing fast" speed) say, real world experience demonstrates the opposite. Web 2.0 "webapps" are slow as dripping molasses and eat memory like they own my whole machine. Input lags, "loading" bars galore for the simplest thing, and that's even when supposed geniuses at Google or wherever are involved. That's Javascript's fault, not HTML and CSS, since those demonstrably still work just fine and aren't
that much more memory hungry than they were years ago.
[EDIT] to be fair to Javascript, there are few or no similarly-robust scripting languages that'd fair much better at half-assedly reimplementing features of their host environment (the browser, in this case). I dislike it for other reasons but it's not because it's slower than its peer languages. And I have plenty of complaints about HTML and CSS for modern "app development" since they've been ill-advisedly pressed into service for that purpose, but speed's not one of them—my browser renders a plain webpage in no time flat.
