I’ve been using Dropbox for quite some time now and surprising, there are still a good many people who aren’t familiar with this service. In a nutshell, it’s a service that allows you to keep a folder in sync in various locations, so you’ll be able to access your files stored within anywhere you are (iPhone, other people’s computers, your other computer etc).
While I’ve been using several online storage services before this, one of the main benefits of Dropbox is that the sync is invisible to me. I just drop the files into the folder and Dropbox automatically keeps it synced with the server, using a tiny symbol to indicate if the file is synced or not. While I really wouldn’t suggest you use it to do backups, I must say that it’s a very useful tool to keep your files backed up in the cloud. One more thing, there’s also built-in versioning, so if you delete or screw up a file on your computer, you’ll be able to pull up a previously saved version of it from Dropbox (again: don’t rely on it for backup, though).