I have been using Delicious for a few years now. What initially interested me was the concept of having access to my bookmarks from any computer. That means from my home computer, office computer, or when logged into a server trying to fix a problem. The tagging part was secondary, though it has grown to be an essential part of the feature set.
I have started to use the tool a bit more lately and have found that I am also using it as a search tool. Not only will it return any items that I have previously tagged, but it will also bring back results from the overall network. The results include a count of the number of other members that have also tagged the page. The value here is that you can get a good indication of which pages were deemed relevant to the community. By starting with those pages, you are much more likely to find what you are looking for.
Do you use it in this manner? Have any other tips? I would love to read your comments!