Delicious is a service for keeping your bookmarks in one place (online), it's social bookmarking.
So let's go with an example; if you have some nicknames from your target, you can search directly on their Delicious profile, all their public links, for example my profile:
Remember that users can mark a link as private, but here is where we can be lucky if they forget to save it as private.
Another way of searching in Delicious, is using target company URL's or IP's, in this example i will use just a standard internal ip:
And look the second result:
The root password in the url :)
In particular cases you can obtain interesting results