It is also very useful when you are collaborating in a project with other people because there is the option to only share one folder with one or more people. Very recommendable!
I have been using Dropbox for a few months now with great success. It is a wonderful help. And every client I have been working with were very happy to use it and all have thanked me for turning them on to this incredibly intuitive file sharing solution. It is also great for syncing between multiple machines. I highly recommend it.