I would argue that it's very useful to learn about data structures and the immutable/mutable distinction upfront (hashtables vs. balanced 2-way trees vs. Bagwell 32-way HAMT vs. "exotics" like skip trees.) I dunno if CL make these as easily avail as clojure

Re: Stacktraces, they have nicer formatting at least, but cutting out irrelevant parts of stack is tough. You can also set

    *stack-trace-depth*

http://dev.clojure.org/display/design/Stacktraces

http://technomancy.us/154