How do LISP macros differ from others?

I constantly hear LISPers boast of the macro capabilities of LISP. How are they different from, say, the macros one can make in C?

>>5
Compiled lisps tend to have god awful interpretter implementations. see: http://picolisp.com/5000/!wiki?NeedForSpeed

optimization via going native is superior to compiler hints anyway.

compiling Lisp is backward. Lisp is clearly meant to be fully interpreted. first-class macros/fexprs are the way of kings.

compiling lisp is stupid. If you want to optimize stuff for a compiler, just write C. I think if you're writing lisp you should be fully aware that you don't much care about performance. lisp machines lost. deal with it.