The biggest thing I loath about SO is when they close threads because the question has been asked before and then link to a thread that nobody has replied to 3+ years.
SO is becoming less and less useful as time goes on because they actually stop questions that need to be re-answered from being re-answered.
In the early 2000s I joined the WELL. It didn't last long. Nobody was having any interesting discussions there. Conversation that went much beyond trite pleasantries was invariably choked off by tut-tutting oldsters telling everyone that everything had been said before.
Over the course of the 2000s, I've had a chance to watch several online communities that I was deeply involved in grow old and die through the same process. I've decided that it's just part of the natural life cycle of an online community for it to die at the hands of its most devoted followers through this sort of intellectual smothering.
So it's maybe not tragic that it should happen to Stack Overflow. It's just sad that it started happening so soon.
Actually, that's a reverse problem to Wikipedia. Wikipedia article quality increases hugely, then as people fiddle with the article the quality rapidly decreases. Then it increases again... ad infinitum. Sort of like a sine wave.
SO is becoming less and less useful as time goes on because they actually stop questions that need to be re-answered from being re-answered.