Yes, the V8 compiler bails out of several optimizations if your function uses eval. You can see this in the profiler: functions which V8 wasn't able to optimize will have an alert sign next to them, and if you click it, it'll tell you what the issue was.
function f() {var x = 99; return function(a,b) {return a(b)};}
f()(eval, 'console.log(x);')
ReferenceError: x is not defined
function f() {var x = 99; return function(a,b) {return eval(b)};}
f()(eval, 'console.log(x);')
99
undefined
Yep, this is as per spec: http://www.ecma-international.org/ecma-262/5.1/#sec-10.4.2 . "Indirect" calls to eval (i.e. assigning eval to another variable, like you did by passing it as a param) are evaluated in terms of the global environment. "Direct" calls, like in your second example, use the local environment.
