I usually prefer to keep my data in a cloud somewhere, or at least in a treehouse or something else which isn’t local disk. Anything not having to depend on sitting in front of the “right” computer.
Currently the treehouse where most of my data lives is a VPS I rent in a datacenter. More specifically I use Subversion to keep my files synced on different computers.
Dropbox being really convenient my big question is on the issue of trust and confidentiality. What kind of (private) data do I dare to entrust them with? Not being entirely sure, perhaps the real question is about which files are non-sensitive enough to be entrusted to any somewhat reliable third party.
Depending on whatever you keep separate backups, which you really should do, the integrity of your data could potentially be a big issue. I have no idea really. I’ll just continue to do my backups, because that is what I do.
Availability on the other hand isn’t something I’m too worried about. If nothing else you ought to have a rather recently updated working directory most of the time.
Having confidentiality, integrity and availability covered, it’s time to get back to the topic of Dropbox being potentially convenient and useful. After all, why else would I want to use it in the first place?
While it’s a nice way to keep my files in sync the biggest benefit of using Dropbox might actually be when you are to collaborate with others. Dropbox makes it really easy to share folders between different users. Yes, Dropbox even has some basic revision control. This might be a good compromise if you work with people whom might not find a real version control system entirely intuitive.