One of the grad students Teaching with Technology Certificate portfolios has a good example of using tagging in Flickr to organize photos that he’s taken which can be used in a course. Jason Brooks from Classics and Ancient Mediterranean Studies department uses a Flickr Stream to not only post his phoots, but to organize them into sets for different themes or different museums/sites.
I don’t know how the course is structured, but I can imagine that he can go to one set on a particular session to show the students the images. Having them organized by topics could also allow the students to go back and review the images by topic (presuming that they are aware of this site). Definitely a good shocase of Flickr for teaching.