This is my first official contribution.
I've created Query Cache contribution that might help improve performance of Zen Cart. It prevents Zen Cart from executing the same queries many times, which can speed up Your store. I tested it on few stores and it usually reduces number of queries from 30% to 60%. Installation instructions and contribution can be found here:
There's also screencast showing how to install this module. Please let me know what You think about it. In case of any issues please contact me via pm or via email (email@example.com)
Note: there will be new version of this module, which will further reduce number of queries sent to MySQL.