Welcome to the Java vs. C debate, previously the C vs. assembler debate, previously the assembler versus hand-coding machine code debate. Computers these days, even netbooks, are fast. Very, very breathtakingly fast.
There has also been a significant amount of work done in VMs, much related to Java, which has delivered tremendous performance boosts to interpreted languages. Google has a very talented VM team working on Chrome's JS execution engine (SpiderMonkey or something, can't remember off the top of my head).
But really, after you get past Wolfenstein done in Javascript (http://www.nihilogic.dk/labs/wolf/ ) how more does the typical user actually need? After that it isn't a matter of CPU cycles, its the programmers coming up with non-painful ways to develop software to use them.