Clojure allows for a lot more chars in a symbol than many other languages. Vim-Fireplace takes care for you by adding lots of the often used additional chars (e.g. ? is the postfix for predicates, symbols starting with : are keywords).
If you are not happy with the choices, you can remove/add simply by creating a ~/.vim/after/ftplugin/clojure.vim file and manipulate the iskeyword there. E.g. set iskeyword-=/ will make the / char a barrier, where word motions stop. Check with calling set iskeyword on the command prompt what is configured.