This is a blog post by technomancy, the original author of Leiningen, exploring Racket as a new language:

http://technomancy.us/175

EDIT: Wrong link. This one might be interesting as well so I've left it here:

http://technomancy.us/169

The TL;DR I would give is this: Clojure is preferable when doing server-side performance-intensive software or in situations where its JVM library reach provides a significant advantage. Racket is a lot nicer for client-side stuff where you need a fast launch, lower memory profile, a GUI, or distributable executables.

If you already have a solid development environment set up and have spent a lot of time learning project management tools, you might have an easy enough time getting started with Clojure, but getting started with Racket tooling is easy even for children.

Clojure is a lot better out-of-the-box for FP, but Racket has third-party tools (like Rackjure and fector) that do a lot to close the gap. On the other hand, Racket has pattern matching out of the box which is really nice, but you can get that in Clojure as well using external libraries. One problem that you can't fix in a library is Clojure's omnipresent nil; Racket does a much better job of ensuring sensible semantics in error conditions, partly due to the fact that pattern-matching is built-in.

Here is a talk by David Nolen comparing Scheme and Clojure (and my summary of it):

http://www.wedesoft.de/clojure-for-schemers.html

  Using either still keeps you in the Lisp universe.  

Also, Greg Hendershott's rackjure library emulates a few "Clojure-inspired" ideas in Racket https://github.com/greghendershott/rackjure

Actually, Racket and Clojure share very little in terms of syntax and semantics. Lisps are like that: they all have parens and frequently that's the end of similarities. Semantics of Common Lisp, Emacs Lisp, Scheme, newLISP - not to mention Shen - are very different. You should treat them as separate languages, especially when learning. So, in short (I went Racket->Clojure), there are no problems if you remember not to write Racket in Clojure and vice versa :)