Dropbox is a convenient, automatic backup system that works on your Macs, as well as Windows and Linux PCs. It allows easy access to files through a Web interface and helps you keep files synced.
Anyone who knows me, knows that one of my biggest issues is backups. Backups are crucially important, so having convenient, automatic backup system makes it more likely that people will perform them. That's why I like "cloud" backup services, like Dropbox.
Dropbox is really useful. It makes doing backups easy, and it makes accessing your files from different computers a breeze. It also includes a great Web interface that allows you to access your files even when you aren't at a computer that's linked to Dropbox. And for iPhone users, there's even a Dropbox app for the iPhone.
With Dropbox, you associate computers to the service. On each computer, there is a folder or directory where you can store files. Everything stored in this directory is then transparently synchronized to every other associated computer. For instance, if you had Dropbox on your Mac Pro, Macbook, and also on a Windows or Linux workstation, you could drop a file into the Dropbox folder on your Mac Pro, and it would be copied to the Macbook and workstation either the next time they came online or within seconds if they're already online (depending on the size of the file and the number of files copied). This allows you to not only keep redundant backups (back up any file on one computer and you can get it on any other associated computer as well as the Dropbox site itself), but it also allows you to easily transfer files between computers as well.
Dropbox has clients for Mac, Windows, and Linux so it is a cross-platform service. And, like the extremely useful rsync tool, it only synchronizes changes, so if you change a 100MB file, it only transfers the bits in the file that have changed, not the whole 100MB file. Not only that, but if the file originated on computer A, then you change it on computer B, the changes are synced back to computer A - a two-way synchronization.
Another nice feature of Dropbox is that you can designate sub-directories in the primary Dropbox directory that can be made public. This means you can store files on your Dropbox that others can have access to, without having to give them access to all of your stuff.
Dropbox is a paid service, but you can use it for free as long as you want if all you require is 2GB of storage. For more storage (up to 100GB), you have to pay a yearly fee. While 100GB won't back up your entire computer, it can back up a fair bit of data. It's obviously not a replacement for a good local backup routine, but it is convenient and very hands-off, which makes it great for documents that change often, especially if your backup routine is spotty.
Finally, the last great feature of Dropbox is that it retains changes in files for 30 days. So if you made a change to a file that you didn't mean to save (or deleted it), you can go through the Dropbox Web site and get the file back to it's state before the unwanted change. A 30-day undo is the default; you can, of course, pay to have this unlimited.
Dropbox is a secure service, but if you're ultra-paranoid, you can back up using an encrypted disk image (dmg) file. If you choose to go this route, be sure to use a sparse bundle disk image. This way, if your disk image is 200MB, you're not transferring big files all over the place, which is more prone to transmission errors, but instead, little bits of the file (called bands) that make up the whole image. It makes for a much more efficient and reliable way to store large files. Using Disk Utility, you can create a sparse bundle disk image, with encryption (128-bit or 256-bit AES), easily.
Vincent Danen works on the Red Hat Security Response Team and lives in Canada. He has been writing about and developing on Linux for over 10 years and is a veteran Mac user.