Digitized archives

A recent article in the New York Times talks about some recent grants by the Levy Foundation to private organisations or institutions to digitize their archives. It emphasizes the positive, that such digitization is unearthing works which were previously uncataloged.

If you are a researcher that had worked with both paper and digital archives, what are your thoughts? Is it possible to conduct comprehensive research from digital archives alone, or must one imperatively see the paper in person?