Here's a not-well-known "feature" of Leiningen. Due to its Maven-style functionality, you can have entries like:
:dependencies [ [some.group/library "LATEST"] ]
in your project.clj, and it will pull the latest library version for you. Great if you are prototyping something and don't want to look up the specific library version to download (EVERY SINGLE TIME.)
However! You should never do this with something you release. Always specify your dependencies explicitly, unless you want to (eventually) run into weird and mysterious breakage.
Hope this saves someone some keystrokes!