Another interesting exploration....
I found Del.icio.us quite easy to use (the biggest hurdle was typing it correctly!), and could see several possible applications in the library. (Now, when the time to apply these applications is going to happen is another question....).
In terms of using del.icio.us to expedidite some of my in-my-office work, I know that my bookmark folders are getting cluttered, and I have not been consistent with putting things with multiple topics in multiple folders. I can see that it would be helpful for me to go through my bookmarked sites, save the ones I still think are useful in my newly-created del.icio.us account, and tag them for easier finding. Since my library offers a weekly preschool story time, and we are often looking for that perfect fingerplay or action rhyme to accompany a particular book, I followed some tags in del.icio.us for story times, fingerplays, etc. I came up with some useful sites by a general search, and noted a couple of people who had bookmarked sites of interest to me as well.
On a research assistance level, my library has 3 public internet computers, and a fourth that we keep open for patrons wanting to search the ipac, log into their library card account, or use the reference databases. There are several sites we've used many time in reference assistance that we have bookmarked on each of the computers for easy access. Saving those sites in a library del.icio.us account and having them accessible at all of the library computers would be handier than adding new sites to the bookmarks folder for each individual computer.
I could also see how del.icio.us could be used to link patrons with web sites of potential interest to them. One concern I had that I did not notice mentioned in the information on the 23things site was to what extent spammers use del.icio.us to draw users to "junk" sites. I did a bit of searching, and it looked like this was more of an issue in the past; more recent articles indicated that since sites are ranked by popularity, spammers who aren't removed simply fall off at the unnoticed ends of the lists.
I did a bit of looking at how the listed libraries are using del.icio.us. McMaster looked like they were using it more for staff sites. While San Mateo's Dewey-organized approach had a certain appeal to me as a librarian, Menasha's approach (organized by subjects) looked a bit more tidy and user-friendly; I would personally tend toward that model of organizing if I were to set up something for my library.