A couple of points (from a top 0.47% user, but that's not why I'm on SO):
* imagine googling for a programming questions and be stuck in 2008 - I don't want to go back
* imagine researching a wittgenstein paper - do you need philosophy.stackexchange.com - probably not; the numbers show, that SO's still the metrics vanguard - I think the demand for the niche sites is certainly there, but large communities have formed around traditional forum sites - and people are happy with that - so there is no pressing need to switch to the new format
* concerning questions - it has been a phenomenon since the beginning, that the simplest answers (C-C C-V the docs) got the most upvotes - interesting hard questions don't earn you much reputation, if that's what you're after - I still get a lot of upvotes for year-old answers, which everybody could have written, while the answers I invested hours in remain relatively untouched; but the main value for me comes from learning by answering questions: try to bring your point across in a few words, collect useful references and show working code - it's like a daily workout equivalent in the tech field
* open questions: I'm trying to make it a habit to answer one hard, unanswered, maybe older question each week - because it's true, the "reputation clock cycle" leaves a lot behind...
* moderation: most moderators have been long around - and I can somehow guess, in which tags a person is active, because I likely saw their comments, answers, flags already a couple of times - can't really blame them for closing a lot of questions - it's hard; if you can, sift through http://stackoverflow.com/tools/flagged and you might know what I mean
* tldr: SO rocks if you're a programmer, for other SE sites YMMV; unsatisfied with closed questions? reopen them or discuss it on meta - it's not possible that moderators don't make mistakes and it's not true, that you can't at least try to discuss specific issues; unsatisfied with unanswered hard questions: find one and write up something great
>"...The answers I invested hours in remain relatively untouched; but the main value for me comes from learning by answering questions..."
More than anything else, that's what keeps me coming back to stackoverflow. Most of the questions I've spent the most time on get little attention, but I learned quite a lot from answering them.
Yes, the organization and search-ability is invaluable. Of course most of the content eventually becomes "geologic" as new material is steadily put down at about a steady rate, the rate of "in the last year" material must become a steadily smaller percentage.
I found at least one of the newer sites, the Ubuntu S/E, to be quite useful for troubleshooting LTS version 12 just a few days after 12 came out.
* imagine googling for a programming questions and be stuck in 2008 - I don't want to go back
* imagine researching a wittgenstein paper - do you need philosophy.stackexchange.com - probably not; the numbers show, that SO's still the metrics vanguard - I think the demand for the niche sites is certainly there, but large communities have formed around traditional forum sites - and people are happy with that - so there is no pressing need to switch to the new format
* concerning questions - it has been a phenomenon since the beginning, that the simplest answers (C-C C-V the docs) got the most upvotes - interesting hard questions don't earn you much reputation, if that's what you're after - I still get a lot of upvotes for year-old answers, which everybody could have written, while the answers I invested hours in remain relatively untouched; but the main value for me comes from learning by answering questions: try to bring your point across in a few words, collect useful references and show working code - it's like a daily workout equivalent in the tech field
* open questions: I'm trying to make it a habit to answer one hard, unanswered, maybe older question each week - because it's true, the "reputation clock cycle" leaves a lot behind...
* moderation: most moderators have been long around - and I can somehow guess, in which tags a person is active, because I likely saw their comments, answers, flags already a couple of times - can't really blame them for closing a lot of questions - it's hard; if you can, sift through http://stackoverflow.com/tools/flagged and you might know what I mean
* tldr: SO rocks if you're a programmer, for other SE sites YMMV; unsatisfied with closed questions? reopen them or discuss it on meta - it's not possible that moderators don't make mistakes and it's not true, that you can't at least try to discuss specific issues; unsatisfied with unanswered hard questions: find one and write up something great