Document Management Systems

I am being directed to implement a Document Management System at our office. We are a 26 person CPA firm with approximately 300,000 sheets of paper annually that are to be scanned, indexed and stored. I am looking at a system with large copy/print/scan devices and a software package to track the items (database of the index information).

For those who have done, are doing, or are looking at implementing a document management system: What problems have you seen, how were they resolved and what do you think are the best ways to make the system work (both technically and with personnel)?

Thanks a ton in advance for your advice.