I'm not an attorney, just the guy who became the resident tech based on serendipitous skills. Sooooo, I won't vouch for our system satisfying all legal requirements for accountability, but I will vouch for the cost effectiveness, simplicity, and general good results we've had for the last few months. We use JST's CollectMax software to track the collections portion of our business, which runs on the above mentioned server, but will be moving to a different box when I shut that down. Since CollectMax has an imaging module, I had tried to turn us into a less-paper office (paperless is just too unrealistic) and we have had some success there, though a couple hundred physical files still circulate daily as has always been the case.
I'll note too that we use Carbonite to backup individual systems throughout the day because I can't get everyone to save purely on the network, nor is that necessarily desirable since deletions are permanent. Also, we have another NAS as well as a large HD on one of the partner's machines that both field nightly backups of documents and images.