Another good solution I've seen in the past relates to very large and complex state forms with many tabs.  You can build many "sub" forms and on the main parent state form represent them via their specific &formname URL.  This allows multiple developers to work at the same time in different areas without as much contention.  Other complexities and limitations exist one of which as Paul points out is transition forms.

We use this same feature for a workflow that has 9 forms with 3 versions (so far...) of each.  We originally started using separate state forms and update transitions for each version of each form, but soon realized that this would unduly complicate the workflow.  The KB mentioned provided an elegant solution for the State forms. 

For the Transition forms, we are using a combination of Form Actions and JavaScript to show/hide the elements that have changed, or to switch between rules that dynamically change certain form elements based on responses to the forms.