DropBox may be great but I'm a paranoid, especially with confidential information. The solution DropBox uses is Cloud computing. Anyone who uses GMail is using a form of Cloud computing.
There are several different solutions one can do with Cloud computing. DropBox reminds me of Windows briefcase and I remember how well that did not work, at least for me.
With Cloud computing the user has to also take in to account how well protected the data is, how well and often the data is backed up and universal access with mobile devices.
DropBox is not entirely free. Here is DropBox's pricing guide located @
https://www.dropbox.com/pricing. The "free" plan includes 2GB of space and for a lot of people that is enough.
Again, being paranoid, I either have to keep 2 copies or trust the DropBox version will be available 100% of the time. That is why I manage my files myself, but besides being paranoid, I'm also anal. An anal paranoid; trust me, it is not a pretty picture.
For Apple users, the .Mac accounts are the easiest but not the cheapest solution. There is a program to turn one's GMail account in to a .Mac "like" account for file storage.
There is SkyDrive for the cost of a HotMail/MSN Live Account and if memory serves me right, it is 25GB. All other comments about backups and cloud computing apply.
Take care,