I love Clojure, and I use it in every project where I have control over the technology, but I do agree with the points raised by Ashton Kemerling.
Clojure is beautiful, and backed by beautiful theories, but its implementation needs to be clean or it will eventually develop enough special cases that its beauty will be ruined. In some sense, you could say this is what happened to Ruby, though there the allowance of "special cases" was more deliberate. I recall, back in 2003, reading the interview between Matsumoto and Bill Venners: http://www.artima.com/intv/ruby.html -- and I thought that Ruby had a beautiful philosophy. But having worked with Ruby for many years, I now see how much it is undermined by the many special cases it allows, and the wild ambushes that its most imaginative features allow (monkey patching).
I don't want to see Clojure go down that path. I want Clojure to remain beautiful, and that means the implementations must also be beautiful. There is a limit on how much the core team can say "That bug is only an implementation detail". If you take away all the implementation details, then Clojure is only a theory, not a real technology that can be used by real people to do real things.
In a truly ideal world, Clojure could be the practical Lisp that pushes itself to bring in as much of the experimental Lisp's beauty as is practical. I would love to see the best ideas from Racket and what Fogus refers to as the Fluchtpunkt Lisps:
http://blog.fogus.me/2011/05/03/the-german-school-of-lisp-2/
These are ideas that can make the world better. I have high hopes that Clojure will be the project that makes some of these beautiful ideas practical. I will be very sad if Clojure ends up like Ruby or Groovy or Scala, becoming a bit too muddy to reach its full potential.