I'm looking at patterns in how people collect different media, and how collecting relates to repeat listening/viewing/using. In the UK, estimates of the average number of CDs in a collection vary between 126 and 178 for men, 135 for women. Are there any similar figures for DVDs or games, or for US markets? I'm still looking.
I'm also doubtful about whether reliable figures exist for the number of digital downloads in collections. There was a report last year indicating that the average number of tracks on an MP3 player is 375, with 50% of players having fewer than 100 tracks. But this is a fast-moving, unstable area, clouded by allegations that 'most' tracks on players are 'stolen', which can't make it any easier to get reliable reports from users. [Update, 22 May 2006: Paul Lamere has just posted some interesting stats on the average size of iTunes collections, and the (high) proportion of tracks that have never been listened to.]
What about repeat listening to music, as opposed to movies/video? This is in no way scientific, but currently there are 15 people on 43 things who want to 'watch every film in my DVD collection', compared with 4 people who want to 'listen to every CD I own'. Are there any statistics on how many times the 'average' CD in a collection is played — and what are the comparisons with DVDs and games?
If there were some equivalent to Audioscrobbler for tracking what people listen to, watch and play, it might be possible to get some aggregate data on this.
In the course of my searches, I came across some interesting screenshots in Flickr. These are based on the new software for helping people catalogue their collections, Delicious Monster for Mac, and its Windows equivalent MediaMan. These enable you to scan in the barcodes of CDs, DVDs, books etc, and then the software pulls in all the cover art (from Amazon) and enables you to arrange your collection on virtual shelves, like this. See the Flickr photos tagged with deliciousmonster and mediaman for more examples.
What's suggestive is how some of these screenshots have 'gone social'. If you look at this image of a DVD collection, you'll see a range of comments both from the owner of the collection and from other visitors. Annotating one DVD, cover a visitor writes "how can you have this and not have Pi", and the owner replies "Technically it's more [my partner's]. Neither of us were too impressed with Pi". Other friendly graffiti includes several tags like "got it" and "Here's looking at you kid" for Casablanca. You don't have to be a visionary to anticipate that these kinds of features will soon be built into the software applications that generate the catalogues.