Having spent 3 years with Clojure, I believe that Lisp macros are just as powerful as they say. But no need to take my word for it ... checkout the paper "Languages as Libraries" by the folks behind Racket.

I've created 3 libraries that I think would be exceedingly difficult, excruciating, or impossible to write with the performance and the level of control over syntax in anything but a very good Lisp:

http://github.com/clojure/core.logic, efficient embedded Prolog in 1K LOC

http://github.com/swannodette/match, in progress implementation of a state-of-the-art OCaml pattern matching algorithm

http://github.com/swannodette/delimc, delimited continuations