The big new feature in the 6.x-2.x branch is that each node/language combination can have a priority so that admins can indicate which are most important. Also has better images to indicate the translation status.
SINCE LAST RELEASE:
* Renamed hook_images() to hook_zoomify_images() to avoid name collisions.
* Added option setting to fix frame size.
* Added setting to pass extra FlashVars to the Zoomify viewer
* Added support for uploading of pre-processed tiles