I have been using Dropbox for more than a year as a sharing service, and the recent failure of my iBook G4 made me understand that it is also a great backup solution. Now, my Dropbox is basically the “My Documents” folder where I place all my files accessible from multiple computers.
After signing-up for a Dropbox account using your email address, you have the possibility to use 2 GB of free storage right away. In the web interface folders can be created, files uploaded or downloaded.
Folders can be shared with friends or co-workers in just clicking a “Share this folder” button. An invitation is then sent by email to the person you want to share with, and after they have created an account the folder is shared.
A software is downloadable for Mac, Linux Ubuntu & Fedora, and Windows, in order to have a Dropbox folder accessible directly on your machine. Whatever is placed inside this Dropbox folder is synchronized with the online storage service and then to any other linked computer, but also iPhone, iPod and Blackberry. You may have folders you share and folders you keep private as a back-up facility.
Drop Box as also a paid service for those who need more than 2GB per month.
Sign-up or read more info on DropBox