I think you're attributing too much of Dropbox's success to simple technical reliability. I did not say anything about their reasons for success. Only what the

I think you're attributing too much of Dropbox's success to simple technical reliability. I did not say anything about their reasons for success. Only what the technical advantages are compared to some of the other file sync services. It really isn't that difficult a problem, Difficult enough that some of its useful features are not matched by other services yet. I have an rsync script that has been syncing my files reliably to an offsite location for 6 years. That's great. But that is one-way sync and not something my parents could use. Dropbox is successful because they made sync technology that is relatively flawless to the average user. Also, there is a network effect. In the longer term, it will be interesting to see if they survive, since Microsoft and Google have been undercutting prices heavily, and as far as I know there is no online Office suite on the horizon (only Microsoft Office integration for business users).