I had horrific experiences trying to get Racket namespaces to work correctly (in Racket, a namespace is a value rather than simply a name). I found I couldn't get files to use the same namespace no matter how hard I tried, and without a specific namespace some code I was eval-ing simply refused to work.

I suspect Clojure lacks this 'feature' :-)

It's frustrating because I'm sure Racket has a lot to offer but not being able to do something really simple (even after hours and hours of trying) completely put me off.