Delicious was one of the best resources for finding articles on niche interests, for surfacing articles that were especially good, and for finding others interested in the same topics as you.
As for two specific examples: Learning Ruby on Rails has been a long, slow, struggle for me. A number of reasons for that, but one of the main ones being that I don't have many other programmers in my area that I can talk about it with. Although there are scores of blogs and tutorials on Rails, it's hard to know which articles are good, and nobody has the time to read them all. So if I was looking for a post on, say, integrating jQuery with Rails, I could do a quick search at http://www.delicious.com/tag/rails+jquery, and I'd find a bunch of articles that had been selected by individuals, for their own use. It was great for finding high-quality content.
Another example deals with niche interests. Delicious made it easy to suss out who is talking about $randominterest. Just by going to http://delicious.com/tag/randominterest, you can see who else is bookmarking it, who's writing about it, and so on. Especially when dealing with, say, fringe programming languages, or uncommon design details, Delicious makes it easy to find people.
Delicious was one of the best resources for finding articles on niche interests, for surfacing articles that were especially good, and for finding others interested in the same topics as you.
I wonder if this could be implemented as an API of websites? (Or perhaps on behalf of websites?) Instead of one single site, you'd have a p2p network of sites using protocols similar to those used for digital cash schemes. Think: a distributed open marketplace of middlemen. A sort of Diaspora middle tier.
Just a side note, but if you're still struggling with Rails, both Zails for Zombies[1] and RailsTutorial[2] are really good. And integrating jquery with Rails is now really easy, since they've moved to unobtrusive Javascrtipt. [3]
I never really cared about the social features. For me Delicious (and now Pinboard) is like a personal knowledge base, supporting my unreliable memory. For example when I want to check my favourite Vim plugins I search for tags vim+plugins+favs.
I have more than 2k entries there collected over the course of the last five years. I only bookmark sites that are for some reason important to me, and have some lasting value (eg. I don't bookmark most HN submissions). I tag everything I save and some of my tags have special semantics that is probably only useful to me.
Ditto for me but not just over my own links. I don't bookmark everything (though I have 6000 bookmarks there) but if I read an interesting article about, say, bioinformatics and it was something to do with Japan, I could hit up Delicious for articles+bioinformatics+japan and 9 times out of 10, be reconnected to content that Google would struggle to find given the same terms.
The difference between Delicious and news aggregators like Reddit / Digg / HN is that the rating of links is a side-effect, not a conscious action.
As a result ranking on Delicious does not prefer yellow journalism, obscure interests or vanity displays; much like Google's ranking but small enough to not be a target for promotion through SEO.
When I bookmark a niche or obscure page, I can see the handful of other users that have also saved it. Because I can click through to their bookmarks, I often find a wealth of highly pertinent and (otherwise) hard to find links on the topic in question.
I haven't done much with it lately, but I still maintain a "daily" tag, containing things I want to read every day. I then subscribe to the RSS feed in Firefox, and which gives me a bookmark I can middle-click on to get my daily reading.
The main problem was that the RSS feed was limited to 15 entries.
I've been using Delicious for storage and management of news links on http://checkuitcheckin.nl/ (a view on public opinion on the Dutch public transport card OV-chipkaart).
I will miss Delicious, I would post a link then use Mechanical Turk to have about 80 to 200 other people also post the same link, then the link would be duplicated on other sites that show "popular" links, social aggregator sites would create a "conversation" about the link, etc. Pretty soon you have 100 sites that link back to yours. Now that is all going away.
