The answer is,
My link log is basically my browser bookmarks, except public. (I don't have any private bookmarks to speak of.) So, for it to be useful, a link description should be reasonably explanatory and have enough keywords that I can find it years later.
The links include things I have read and might want to re-read, things I have not read but I think I should keep for future reference, things I want to read soon, things that look interesting which I might read, and things that are aspirational which I feel I ought to read but probably never will.
(Edited to add) I should also say that I might find an article to be wrong or problematic, but it still might be interesting enough to be worth logging - especially if I might want to refer back to this wrong or problematic opinion for future discussion or criticism. (end of addition)
But because it is public, I also use it to tell people about links that are cool, though maybe more ephemeral. This distorts the primary purpose a lot.
It's my own miscellany or scrapbook, for me and for sharing.
A frustrating problem is that I sometimes see things which, at the time, seem to be too trivial to log, but which later come up in conversation and I can't cite my source because I didn't log it or remember the details.
Similarly I sometimes fail to save links to unusually good blog articles or mailing list messages, and I don't routinely keep my own copies of either.
Frequently, my descriptions lack enough of the right synonym keywords for me to find them easily. (I'm skeptical that I would be able to think ahead well enough to add them if I tried.)
I make no effort to keep track of where I get links from. This is very lazy, and very anti-social. I am sorry about this, but not sorry enough to fix it, which makes me sorry about being too lazy to fix it. Sorry.
What I choose to log changes over time. How I phrase the descriptions also changes. (I frequently change the original title to add keywords or to better summarize the point. My usual description template is "Title or name: spoiler containing keywords.")
Increasingly in recent years I have tried to avoid the political outrage of the day. I prefer to focus on positive or actionable things.
A lot (I think?) of the negative "OMG isn't this terrible" links on my log recently are related to computer security or operations. They fall into the "actionable" category by being cautionary tales: can I learn from their mistakes? Please don't let me repeat them?
Mailing lists. I don't have a public list of the ones I subscribe to. The tech ones are mail / DNS / network / time related - IETF, operations, software I use, projects I contribute to, etc.
RSS/Atom feeds. I also use LJ as my feed reader (retro!) and sadly they don't turn my feed list into a proper blog roll, but you might find something marginally useful at http://fanf.livejournal.com/profile?socconns=yfriends
Hacker News. I use Colin Percival's Hacker News Daily to avoid the worst of it. It is more miss than hit - a large proportion of the 10 "best" daily links are about Silly Valley trivia or sophomoric politics. But when HN has a link with discussion about something technical it can provide several good related links and occasionally some well-informed comments.
Twitter. I like its openness, the way it is OK to follow someone who might be interesting. On Facebook that would be creepy, on Linkedin that would be spammy.