I'm sure there are a load of posts professing their love for Delicious Library. It's pretty sweet. I downloaded it just after Christmas for no reason other than I thought it was really cool, but since then I've started to realise that some features could be real-world useful. Making an inventory of your possessions could be useful for insurance purposes, which is a most sensible use of this great program. I can also use it to track items that I've lent to people, because it integrates with Address Book on OSX.
I borrowed a bluetooth barcode scanner from my friends at Internetware and used that to zap over 500 items - books, DVDs, CDs - and Delicious Library ate them all up. It can be configured to read out the title of the item you've scanned so you can confirm it's been inserted correctly, which was great for us as we bleeped our way through our bookcases in another room. The novelty of it didn't really wear off either, in fact I found myself looking for more stuff to scan even when I'd finished the bulk of the items.
I've now got an attractive, searchable database of many of my possessions, and the Delicious Library publish feature means I can expose it to the web. My library currently holds 442 items and certainly gives a good look at my interests - most of my books are science fiction, for example.
When adding new items, Delicious Library offers the ability to use a webcam (such as my iMac's built in iSight) as a barcode scanner. This feature's been pretty disappointing and it requires quite a few attempts to get it to work, but adding items manually is pretty straightforward. New items can be automatically filtered using the smart shelf feature, which currently pulls all sci-fi and fantasy stuff into a separate area. In short, Delicious Library is much recommended!