As if by magic, Thing 10 actually dealt directly with the sentiments expressed in my previous blog entry (I didn't sneak a peek ahead, honest, guv!). So, yes, social bookmarking sites can be used, and indeed already are being used, by institutions such as libraries. I think it's a pretty good idea, although it works on the assumption that we are all delicious (sorry, "del.icio.us"... or have they dropped that now?) users. I suppose really you could achieve the same result by providing links on a web page.
The real advantage to sites like delicious is the interactive element, demonstrated by the "networking" task. In doing this, you effectively set up an ever-growing, constantly updating "favourites" folder all related in some way to the topics you chose or the things you like. I can see huge potential, although I wonder if you were to start networking with, say, five or six users or institutions (much like the RSS feeds for blogs) how would you ever keep up-to-date?