The newsroom at washingtonpost.com the website of The Washington Post is not so different from that of a print newspaper with one notable exception: At a time when newsrooms across the country have empty desks from recent buyouts and layoffs staff numbers here are expanding to fill every available nook and cranny. Washingtonpost.com is a success story in an industry where the divide between vibrant online ventures and shrinking print products is increasingly sharp. But even the Post has no idea how long that success will last how much money it can make from the venture or who exactly its competition is.