A lot of users want to share their photos and are blissfully unaware of FaceBook/Flickr. You said it yourself: >But there are always people who are looking for a better solution. Don't dive straight in, work out what users want that flickr/etc doesn't offer - and do that.
blissfully unaware of fb? considering photo tagging (and then showing up in the news feed) is just about the killer app on fb - and its 150mil users growing at 10mil per month -- I'm tipping this is a reasonably small market... (ie - savvy enough to use/explore your site while not knowing about fb/flickr/etc)
Yes, indeed. I have a few friends who use fb and after some time they tend to think that "everyone is on the facebook". ;-) But actually not. There are many more people who don't know what fb is, or they don't use it.