Beth Kanter from TechSoup.org has published an extensive guide to using Flickr.com. This guide provides examples of different scenerios where organizations can use Flickr to upload, share, organize and find photos.
The document features a step-by-step guide to set up a Flickr account and get the most out of the community features the site offers. The guide includes tips for uploading, tagging, organizing, grouping and sharing photos. Flickr has soem great extra features that make it one of the best photo sharing sites. The site has a built-in feature where users can create a map showing where the photos were taken.
There are some great external links on this document. One of the most fascinating links is to a photo group (called "Entitled") devoted to pictures with unique titles. There are also links to some good tracking sites so you can monitor who views your photos.
According to Flickr's Director of Community, Heather Champ, there are more than 2 billion photos on Flickr and over half their users are international. The photo site is a great resource for nonprofits to share information and there are a number of creative ways to use the site as part of your communications strategy.
You can view the guide here. I've also attached a .pdf version to this document.