First heard about Flickr here at Seth's Blog, so I decided to sign up for an account and give it a try.
Here are my observations:
1. Sign up is really easy. When you sign up you are choosing a screen name (like AOL instant messenger) that will be used on the Flickr sharing services. Bear that in mind if you are being creative.
2. All of the demographic info (at least at this point) is optional.
3. There is no stand-alone application; everything that Flickr does operates within a web window: photo uploads, viewing permissions, chats and conversations, etc.
4. You do not seem to be able to externally share your Flickr photos outside of the Flickr network. In other words, you cannot upload a photo and assign it an external URL that can be accessed directly.
5. There are different groups of people that you designate into groups. Those groups make up your permission list. It's that simple.
6. You can set up blog integration so that you can blog about photos that you've seen on Flickr. I am assuming that the blog displays the picture (haven't tried it), so maybe I'm wrong about number 4 above.
Conclusion: It's another social networking site, but perhaps it's more useful than some of the others. Imagine having your whole extended family online as part of your trusted group; instead of mailing out photos or even e-mailing, everyone could upload their photos for everyone else to look at and comment on. I don't really know if I want to share my pictures with complete strangers, but that's just me. Certainly worth checking out.