Most of your document management systems allow users to pull stored docs off a a server to do what ever they want with it but limit direct access to the originals on a secured server. There is a company called Ventura that seems to be a leader in providing customized and 'off the shelf' doc management systems for high profile corporations, I know longer have their URL but if you happen to find it there was good info there on what a high end doc management system should be.

As far as alternatives, I recently bid a intranet doc management system job using Steve Black's wiki software. (See http://wikis.com) The client was majorly impressed with the proposed solution because of the simple browser interface and cheap price for great flexibility. Unfortuantely they had already seen the Ventura demo's and wanted in on a whole suite of management tools in addition to a doc managmnt system.

One other thought and I'm not sure how viable this is... 10 years ago I set up a custom doc management system in a few short days using a tool called FileMake Pro. That system lived for over 5 years with very little maintenance and very little extra attention from. Plus it managed hundreds of government contract documents. FileMaker was a flat file database product back then, and last I seen it was still around and claiming to be relational now.