Dropbox is a free service that lets you bring your photos, docs, and videos anywhere and share them easily. Never email yourself a file again!
The main benefit of Dropbox is its client applications which are available for Windows, Linux, and Mac. All you need to do is create an account (either free or paid one), download the client app, install it on your computer, and you're ready to go.

Dropbox gives you 2GB of space for free account and you can earn more spaces by referring your friends to use Dropbox. Dropbox is now doubling the amount of free space you get per referral to 500MB, compared to the previous 250MB per each referral. This is retroactive and applies to referrals you've already made.

Quoted from Dropbox blog:
How much space is that, exactly? For every friend you invite that installs Dropbox, you’ll both get 500 MB of free space. If you’ve got a free account, you can invite up to 32 people for a whopping total of 16 GB of extra space. Pro accounts now earn 1 GB per referral, for a total of 32 GB of extra space. Have you already invited a bunch of people? Don’t worry. Within a few days, you’ll get full credit for every referral that’s already been completed. Boom!
Well, what are you waiting for? Create a free account, tell your friends, and get more spaces on Dropbox!

Install Dropbox Client on Ubuntu
Simply download the installer here and install it once downloaded.

If you are using XFCE, you might want to read my post about enabling Dropbox copy public link on Thunar File Manager.

Enjoy :)