>"The difference between the two? Yahoo! Bookmarks is for private online bookmark storage. Delicious is for those narcissistic enough to share their bookmarks with the rest of the world, Web2.0rhea-style."
...or, coming at it from a different angle, Yahoo Bookmarks has a predictably clunky interface whereas the relaunched/redesigned Delicious has improved on an already excellent service.
Admittedly, I rarely use the social/sharing elements of Delicious, but it's a powerful tool for various groups of users and I find that it functions brilliantly as combination of online bookmarking and edited highlights of my web history. If anyone finds the links I've saved to be useful, then so be it. And remember that you don't have to share at all - the option to keep all of your bookmarks personal and hidden is there, should you wish to enable it.
And it has managed to restrain itself admirably by not pretending to be a portal for the bored, or degenerating into a faddy "add me, add me" hive-mind "community" of "friends".
It's sense of purpose is self-evident and I see Delicious (along with Flickr) as one ofthe jewels in Yahoo's crown. Both those services are also a refreshing alternative to Google's rival offerings.