Dropbox has been kind enough to offer 5GB of free space for its cloud-based storage service. Free users receive 2GB of space, and this 5GB additional space bumps it up to a nice 7GB.
It's 'free' which means it comes with some restrictions such as users must download and install the 'experimental' Dropbox client. Users must utilize Dropbox's new automatic photo import feature to upload photos. This feature is the reason behind the promotion, where Dropbox want to iron out the bugs in this new venture.
Once you've completed your first photo import, Dropbox will give you an additional 500MB of space. For every 500MB of photos you upload afterwards, Dropbox will give you an additional 500MB of storage, until it reaches the 5GB additional storage mark. The 5GB of space is permanent, even when the beta ends.