Simply put, Dropbox gives you the ability to keep your desktop files synced with “the cloud”, and your other computers. Think of it as online data storage(backup), file sharing, and file synchronization, in a simple no fuss implementation.
A folder created by the Dropbox installation exists on your computer(s) to handle all the heavy lifting.
What makes this service so attractive is that you can can use it on virtually any system, anywhere. Dropbox is available for Windows, OS X and Linux as a client. Your files are also available through their web interface. Additionally, they provide a mobile formatted version of the site for iPhone and Windows mobile devices. So you can access your files on the go.
Free accounts can have up to 2 GB of storage space, so it's perfect for your most important small to midsize documents/files. $9.99 a month gets you a 50 GB account. $20.00 per month buys you 100 GB. Honestly, the free account, is usually more than enough for most folks, but it's nice to have an upgrade path for premium space.
Check it out and sign up for free:
Dropbox