Dropbox is a brilliant and extremely useful online storage service. Online storage services aren’t anything new and what makes Dropbox special is it’s ease of use, speed and how it seamlessly integrates with your host operating system.

Basic account registration is free and you get an instant 2GB storage. Invite your friends and every friend that joins earns you (and your friend) an extra 250MB up to a maximum of 3GB in addition to your initial 2GB.

Pro 50 account provides 50GB storage and costs $9.99 per month or $99 annually. Pro 100 account provides 100GB storage at a cost of $19.99 monthly or $199 annually.

The service can be used as a simple online storage tool via a web browser, to upload files from one computer and then access those files via a browser from another computer. But Dropbox is much more than that – it can be used to share files/folders with other people, keep your data synchronised between multiple computers and easily create online photo albums.

The best way to use it is to install it on your computer, where it seamlessly integrates with Finder/Explorer. Once installed, it can be used just like a regular folder and you can add sub-folders and files to it. When a file is added, it instantly starts to synchronise with the online service, freeing the user to carry on working on other tasks. This is a brilliant tool for users with multiple computers, who want to keep certain data files synched. Store such files in your Dropbox folder and you don’t have to concern yourself with uploading files from one computer and then downloading to another. It all happens automatically without any user intervention.

Files added to the special Public sub-folder can be shared with others – just right-click on the file, copy the public URL and send the link to whoever you want to share the file with.

If you’re working on a project, create a shared folder for storing documents and invite collaborators to share this folder. Uploaded changes are instantly visible to other project members. As soon as one collaborator modifies the contents of the shared folder, the changes are automatically pushed to other collaborators’ Dropbox folders instantly, brilliant! Accidentally deleted files can be easily recovered.

Another really nice feature is that any images added to the special Photos folder are automatically created in to simple photo albums, with public URLs available for sending to friends and families.

Have a look at the tour for full details and explanation of the service. There is also a screencast available which clearly shows all the major features.