This is a perfect example of why you should ignore the naysayers and "experts" on HN when you first pitch your idea or product. Also, a great example of why the best startup ideas look initially like bad ideas (http://www.paulgraham.com/swan.html)
Let's be fair though, there's a survivor bias here. It's probably more dangerous to blunder on and simply tune out any criticism.
If you look at the top rated comment on that thread it is certainly a valid criticism, namely that corporate computers are often locked down and won't allow installation of third party software without getting sign off from IT. In the case of dropbox that managed to sidestep this by mainly targeting smaller businesses and individuals and also have the fall-back of letting users access their files over the web.
