Well in the first case you are using ( ) to wrap the object you want to execute with the next set of (), and in the next case you are using operator that takes one argument (negation operator !) and you are making it implicitly wrap its argument (funcion) with ( ) so you actually get !(function () { })(), execute the function, and negate the result it returns. This can also work with -, +, ~ in the same principle since all those operators take one argument.
!function () { /* presumably the same magic happens */ }()
-function () { /* presumably the same magic happens */ }()
+function () { /* presumably the same magic happens */ }()
~function () { /* presumably the same magic happens */ }()
Why would you want to do this? I guess it is a personal preference or if you have big .JS and want to save 1 char per anonymous function call... :D
