I have surveyed Documentum, Vignette, OpenMarket and Interwoven. And I think Interwoven is the most flexible among them.
==Interwoven==
The good:
1. You get to manage all your documents/files (static webpages), application code (dynamic webpages) and data in your company at the same platform.
2. It has a very flexible workflow engine that you can customize in a variety of ways.
3. It can be integrated with a whole bunch of production site packages.
The bad:
1. Like all "infrastructural" products, you may have to spend some efforts implementing Interwoven. (But I think its flexibility makes this worthwhile.)
==Vignette==
The good:
1. Its a typical end-to-end solution, they've got every "function" you need. (But you must adapt their way of doing it.)
The bad:
1. It's a DB-based product that you may want to consider the transference cost when you decide to drop it.
==Documentun==
The good:
1. A very good document management product.
The bad:
1. Just manage documents.
==OpenMarket==
Just sucx