(Admins: please delete this page. Noone needs it.)
Module page: http://drupal.org/project/crumbs
The 2.x branch of Crumbs contains some modifications to the API, which are not backwards compatible. The 1.x is tagged "unstable" for a reason.
Things you might be interested in for upgrade and downgrade:
- Bad: Any custom module that implements the 1.x crumbs API will need to be modified to work with the 2.x branch.
- Good: The 2.x API had to be considered a "moving target", but we are now (mostly) beyond that phase.
- Good: The module will attempt to port your configuration of weights from 1.x to 2.x. The 1.x configuration will be kept in the database to allow an easy downgrade.
- Good: It will be possible to upgrade and downgrade between the two branches at any time. The configuration of weights will not be lost, as long as you don't uninstall the module.
- Good: Your modules can support old and new API in parallel. They won't interfere with each other.
Probably this information will go into an UPGRADE.txt eventually. But it doesn't hurt to have it in this page as well.