Dropbox is a very useful online service and its developers provide a Linux client, but there is a small problem with the latest versions in Ubuntu OSes.
Normally, you can install Dropbox in Ubuntu from the official repositories, but the build is a little outdated. It will work just fine, but if you want something newer you're going to have to download the appropriate deb file.
The installation works without a hitch, with one exception – you won't get the Dropbox indicator in the upper right-hand side. This is easily fixable by installing just one library. Open a terminal and enter the following command (you will need root access): sudo apt-get install libappindicator1
When the installation is complete, just log out and log in, and the indicator should now be visible. Enjoy!