It's a mystery to me why I haven't set up a Delicious account sooner, given that I can utterly see the point of it. While there are some links I only really use at work, and some I only use at home - which can therefore be cheerfully be bookmarked in the browser on home and work computers - there are some that I don't use everyday, that I won't remember without prompting, and that I might want to access from anywhere. Foremost in this list would be 'articles I saw somewhere-or-other but didn't have time to read immediately'. With these all neatly stored away in Delicious under 'toreadandinwardlydigest' they'll be available to me whenever and wherever I have a chance to read them. Very handy.
I also like the design of the site - clean, clear and simple. I like the ability to organise tags into bundles, the choice between viewing them as a list or as a cloud, and between them sorted aplhabetically or by frequency of use. The tools are handy, too, although I'm not sure I'll go all the way and embed a tag cloud or bookmark-roll on my own blog. What do you think?
I can definitely see the merit of using Delicious in a library or other information-management environment. To my mind, it's a great way of disseminating links and resources. Because it's a dynamic tool, users can pick out the links they're interested in by using and combining tags, rather than having to read all through a list put together by someone else: there should be a higher wheat-to-chaff ratio for each individual user than on a static page. From a librarian's perspective, it's also probably easier to maintain than a page of links written in a CMS or in straight html. One disadvantage of using Delicious is, however, that you will be referring users to an outside site if they want the full functionality of the service rather than just a 'latest links' widget embedded somewhere else. This means that they might not realise that the service is being provided and managed by the Library.
I haven't really investigated the 'community' aspect of Delicious yet, so I can't comment of the usefulness of being able to search other people's tags. As with so much, I expect that the value is dependent on the like-mindedness or otherwise of you and the other however-many-millions. It's probably fun to search, but I'd be surprised if it was an efficient search tool.
One final thought: where do I bookmark the Delicious homepage?
P.S. Magistra et Mater's thoughtful post on Delicious comes highly recommended if you're looking for another opinion.