Flickr
I see lots of talk about Flickr which I don't really understand - photo sharing websites are nothing new, and Flickr itself doesn't seem that different than our own ZIMoBLOG (also a .NET app).
I've got a SOAP API for ZIMoBLOG, a Windows Forms based bulk posting tool, even a screensaver that uses photos from your collection of online photos as a screensaver. Still not sure what to do with it all.