This week's book giveaway is in the Other Open Source APIs forum. We're giving away four copies of Storm Applied and have Sean Allen, Peter Pathirana & Matthew Jankowski on-line! See this thread for details.
Clojure's design draws heaviliy from several amazing languages - haskell, ocaml, erlang, common lisp, scheme, etc.
I haven't personally used Haskell in any real project, so I can't comment directly. However, I do believe that Clojure's macro system has advantages that other languages don't have, and can't provide in the same easy way.
What I mean by that is that in Clojure, being a LISP, building mini-languages (DSLs) on top of the core is a natural design pattern. There is language-level support for this, with the macro system. Also, being functional in nature, designing systems in a bottom-up manner is far more natural and results in more expressive and elegant code.
Further, Clojure has explicit support for state-management (safe from multithreading issues). These constructs are much easier to understand and use than, say monads in Haskell.
Well, for one thing, all core data-structures in Clojure are immutable, which is not true of CL.
Further, Clojure has a built-in STM system which allow for safe state management (be it of a single thing at a time or for multiple things in a coordinated transaction). This doesn't exist in CL, unless you use one of several STM libraries out there. Even then, it isn't automatic, and requires careful discipline from the programmer.
Clojure was designed from ground-up to support safe multithreading.