That's the opposite!

Using const references is a good idea for large objects (say, 16 bytes and more).
For very small objects (smaller than a pointer), if you're lucky, you'll not loose performance.
But it is quite probable that the compiler will generate more code, slower code, and use more stack memory (if the argument is not a lvalue).
And, moreover, it is very hard for the compiler to optimize the const-reference thing when the function is used across translation units boundaries (at least, for most compilers), because it must respect a calling convention, and can't know whether the function, internally, gets the address of the const reference.
In that case, the compiler can't replace such const-reference by a simple value.

Please read my posts on these two threads:
http://www.codeguru.com/forum/showthread.php?t=339608
http://www.codeguru.com/forum/showth...=392134&page=2