I have been using Flickr to keep my photos for quite some time now. I have been so impressed by their service that i have opted for a paid membership. I have been putting up photos there ever since. Here's an interesting article on how the open source technologies are helping Flickr work.
Also, here's a link to an interview with Stewart Butterfield (CEO, Flickr.com) on how flickr went from being a small startup to the 270,000 users + 4 million plus company it is today.