Honestly I'm a bit of a social media Luddite, but I've bounced around different fora during different parts of my life one of my favorite being Ace Combat Skies. Back when I was in middle school, I'd browse endlessly throughout the forums they set up for each game on Gamespot. There used to be all manner of hidden gems, ranging from threads with witticisms related to the game, to very old games with a single-post topic claiming its starter had dominion over the rest of the board, to entire communities hollowed out of the Sonic Heroes board, complete with roleplaying, art, jokes, and everything in between.
For better or for worse, forums have given way to social news sites such as Reddit, or imageboards like 4chan, or even blogs like... eh, I don't read any. But it's just not the same. There are no personalities, no sense of following the link there and thinking to yourself "I'm home." That's one of the key reasons I opted to join this site.