It slipped today that Yahoo! will soon to shut down Delicious, née del.icio.us, the social bookmarking site. When it became obvious a few years ago care and feeding of the site had more or less stopped, I fled the service, like many other users, for the clones.

Delicious was important for two reasons. It was all about discovery—what your friends and the other interesting people you were following were reading. Predating Digg and reddit, it was the first service to do what Twitter and Facebook now do so well—point you at a URL you will probably be interested in, by virtue of having been vetted by your social network.

It was also important because it popularized "folksonomies," the now-ubiqitous act of tagging items as a lightweight, and therefore actually used and useful, alternative to categorization. You can thank del.icio.us for tag clouds and high-quality Flickr searches, for example.

Delicious was internet plumbing, but it never became essential internet plumbing. You could automatically update your blog from it with what you were reading (and so many people did that they stopped writing in long-form and just published from their Delicious accounts a link and some commentary, it resembled an early Twitter-esque microblog in that way). Lots of people offloaded their brains to it (especially reference material and how-to guides and programming tips, learning stuff they intended to come back to later). But unlike its big Yahoo! sister Flickr, which has become an essential pipeline for web images, Delicious never grew much beyond what it was in the early days, never caught fire as a social network in its own right despite millions of users. Whether this was due to neglect or mismanagement or cluelessness, in any case, it was a missed opportunity, to become essential.

People are wondering if Yahoo! understands what the shutdown means for their reputation, when it comes to safeguarding user data or being reliably available. It's a classic data liberation problem, and if Yahoo! doesn't make it easy for users to take their bookmarks out of Delicious (or their photos out of Flickr for that matter), folks might not trust a future Yahoo! product with their data.

Bookmarking lives on despite the fact that you can pretty much Google anything, replacing the offboard-brain reference index, and that social network-based discovery is now dominated by Twitter and Facebook—people still like being able to curate their own little slice of the web. pinboard.in is one post-Delicious site that looks particularly promising and vital; tellingly, it refers to itself as anti-social bookmarking.

Farewall, Delicious—for a few years at least, you were essential to me.