Re-including link to using Zimbra Desktop 2.0 Beta 2 for Zimlet developing:
ZCS 6.0:Zimlet Developers Guide
ev Environment Setup - Zimbra :: Wiki
As for the cache, ZD does cache Zimlet
JS code, i18n properties and CSS content. When running in Development Mode (?dev=1), you can bypass the cache. But to clear the cache, you can delete the files in the following directory:
c:\Documents and Settings\{user}\Local Settings\Application Data\Zimbra\Zimbra Desktop\data\tmp\diskcache\zimletres\latest
In that directory, you'll find files with unique names (ending in .javascript and .css extensions). Delete all the files.
Reload ZD and those files get rebuilt and the old zimlet code that is hanging around in the cache should be gone.
After reloading desktop and the files are recreated, you can browse to the newly recreated cache files like this:
http://{your-desktop-url}:{your-desktop-port}/service/zimlet/res/Zimlets-nodev_all.
js?language=en&country=US