4- Flickritis

I think Flickr is great in that you can post pictures for all or some to share- and retrieve them by tags. I'm not as sure about the groups, unless you're really interested in one area, and want to retrieve all photos from those users and discuss with them. The Creative Commons licenses are great, so you know which photographs can be used in what way- I can see making use of this for work-related pictures that might be needed.