Workflow does keep version history of published workflows. You can access them from the Workflow Administration Console > Workflows > Workflow Definitions. You'll see a column with current version numbers for each workflow. When you select it, you can view the version history on the right side, and download specific versions.

Forms unfortunately doesn't have this feature. However, I think the upcoming BPM Server will take care of that, since both forms and workflows will be managed from the same module (I think).

EDIT: We currently use git to manage our Forms Business Process versions. We basically export each BP to the same location, overwrite the existing XML, then commit it to the git repository. We have had to roll back to a previous version of the BP a few times and it has been pretty useful. Git is a specialized tool though, so it has a learning curve.