Yesterday, I bought a copy of Delicious Library, which is a program for managing collections of your stuff. 
I can use my iSight camera to scan in bar codes of books, DVDs, software, CDs and they appear in the library as icons. It loads all kinds of information about each item via the internet, probably from Amazon, and also has a suggestion feature that shows you similar items.
You'd think that a collection management tool would be, well, a little dull but it's little things like the icons are not a set size so that you can use a slider bar to scale the images in real time, much like the Mac OS X Dock. It's incredibly slick, and just fun to play with.
I think that software that is fun to use creates very interesting scenarios, where users are encouraged to play with it. "Play" is the exact right word, although "explore" is suitable too, with applications like Google Maps and Google Earth. You get to see cool new things, and there isn't any chance of breaking it.
Anyway, I can see where Delicious Library is going: connecting to your friends' collections and doing trusted recommendations, borrowing (it hooks in with iCal and Contacts to show who has your item and for how long), revenue sharing with Amazon.
I'm adding it to my Brilliant Code list.
Yeah that app just drips of cool. Even their web site is hip.
Can you index non-physical media?
If you mean software that you've downloaded, etc, sure. You just won't be able to scan it in, but you can add it manually. You can also create your own catagories (i.e. "sports gear" or "severed heads").
What I'd like, which might already exist, are labels that I can apply. For example, labelling a movie as "Sci-Fi", "Action", etc. Each item can have multiple labels, like Gmail, so you can find things by genre or mood.