I'm a little confused - really great execution (!!) but I don't see the business sense. I'm not sure how this differentiates itself from other file hosting/pho

I'm a little confused - really great execution (!!) but I don't see the business sense. I'm not sure how this differentiates itself from other file hosting/photo sharing sites. For instance can you have private photos on Flickr? At the very least there are things like drop box as mentioned. What about people who tend to share photos through Facebook? Besides which, what is the monetisation strategy? Freemium? What features will be added? There must be some sense or it wouldn't have got YC investment - maybe the idea is to execute this so well that Google buys you you as I don't think they have a good photo sharing method yet and it would be a great way to expand?