I still think it might be a bit obscure for the casual Web user though. I think the problem lies with what I assume is an attempt to over simplify the experience. I say this because I've sent people to the site and their first comment tends to be "So what are all these links?" (actually, their first comment is usually more like "Delicious? So is it www.delicious.com? What? del.icio.us? I don't get it." Note to Yahoo, who recently purchased Del.icio.us, consider a name/URL change. It was cute for a while there, but...)
One of the reasons I've become so enamored of it is what you can DO with your bookmarks once you start collecting them. You can put them in an RSS feed for instance. Or you can send someone all the bookmarks you have tagged with, say "recipes" just buy sending them a link to http://del.icio.us/username/recipes.
Another example: I recently did a bunch of research on podcasting directories because we were in the process of launching podcasts for my company. Every time I found a directory we might want to post our podcast in, I clicked my Del.icio.us button, described the site and tagged it with "podcast" and "directories." When it came time to share what I found with my boss, I just sent her a link to http://del.icio.us/napdynmite/podcast+directories (feel free to click on that, it works).
I also like the fact that I can tag bookmarks with the names of people in my network and they'll get my bookmark in their inbox automatically. Great for team research as well as just fun.
Anyway, check it out at http://del.icio.us/ if you haven't already. Make sure to get the browser buttons here: http://del.icio.us/help/. It makes the whole process seamless and almost habitual.