The Janus Nature of Document Management
A service is something that has to be delivered as a basic business enabler (think help-desk, dial-tone, etc.) There is really no business case for service provision; it's simply a cost of doing business. The only case to be made is to assess the Value-at-Risk for major initiatives (e.g., process improvement, etc.). Document management is different from other investments in that it is unlikely to reduce operational costs. For example, one could replace a phone system based on the costs of the existing system or the possibility of it failing. These criteria aren't applicable to document management.
The other side of document management is projects. There is a clear business case to do something but by definition that project effects only one business unit or business process. The danger is that the strategy will ultimately fragment the business due to our inability to bring common information facets together.
Basically, you need to define document management as a service before you can really initiate projects. Doculabs has played with this idea in the past. In particular, it provides an interesting operational model for what to put in place before expanding into actual process improvement initiatives.