So, I use Flickr very casually. I take pictures with my cellphone, and when I have a particularly good picture, I push it to Flickr. If I go to an event like a wedding, I often take a lot of pictures, then put them all up for folks to see. Otherwise, I've just thought of Flickr as a linear blog.
But now, I'm up around 500 pictures over the last few years, and having them unsorted was a disaster of information design. Flickr offers Sets, Collections, Groups and Tags, and that was a bit confusing. Here's what I've come to. It's probably very much overkill, but assuming I'll eventually have a few thousand photos in there, I'd prefer to overkill the system up front instead of having to do lots of work shoehorning this into shape later.
- A set is a bunch of pictures, all owned by you. A picture may be in many sets. A collection is a group of sets or (xor) a group of collections.
- Separate from the collection/set hierarchy, a group is a bunch of pictures, with one or many owners.
- Separate from the collection/set hierarchy, separate from groups, are tags, which are similar to tags on many other web applications; they're searchable labels that anyone can apply to any picture.
- Collections represent large themes. "Places", with subcollections of "Pittsburgh, PA", "Washington, DC", "Other Locations", for example.
- Sets represent a time and place. "2008 - Air & Space Museum", "2007 - Ocean City, MD" are examples.
- Other sets are ongoing, without necessarily having an associated time. "Family Pictures", "Stuff I'm Selling", "Scanned Pictures" fit here.
- Groups are ways to share with other folks at an event. "2008 - Mark S's Wedding" is a set, but "Mark S's Wedding" is also a group, so that everyone at the wedding can aggregate their photos in one place. It might be nice if Flickr let you add a set to a group, but no such luck. I'm assuming that's not there, because it'd also water the quality of photos in many groups.
- Tags are a way to make searching much, much easier. Years (2005, 2008), camera settings (grayscale, IR), locations (LA, DC), other descriptions (Club, Yellow, Steelers) all fit here. Not so much worried about sorting through these later as searching through these later.
Edit: I'm actually pretty horrible with the tags, as searching isn't often a problem for me.