I met Drew, one of the founders of Dropbox, a few years ago at Barcamp Boston. If I remember it right, he said that the initial dropbox.com owner was just some random dude who was planning on starting some sort of venture related to dropboxes, hadn't done it yet, but didn't want to sell. My impression was that he got the domain some time before Dropbox launched, and at least initially, he wasn't doing anything particularly irritating other than letting a short domain name languish (not that bad, in the big picture).
From the PDF in the link, it sounds like the original owner then transferred the domain to a third party, who then ran ads for Dropbox's competitors, leading to the legal wrangling.
More or less the opinion I got from it, although the third party seems more like a service the guy used. The guy was clearly using Dropbox and its brand name for his gain, but I can't easily get behind this as good thing when he had domain name first and legitimately. If he went ahead and made a company of his own called dropbox he might well have been fine, who knows. Just felt compelled to comment because the anger directed at the guy seems a bit unfair - it was Dropboxes choice to start a company up called that when they knew they someone else owned the domain.
He probably would have been fine if his business was airdropping goods or something else that can be construed as "dropbox" but in a realm sufficiently different from file syncing. He certainly couldn't have started a file syncing company called dropbox, that seems like obvious trademark infringement. Mere registration of a domain doesn't create a trademark.
From the PDF in the link, it sounds like the original owner then transferred the domain to a third party, who then ran ads for Dropbox's competitors, leading to the legal wrangling.