One commonality is that eberything you mentioned is a site that specifically gathers people around a common topic/interest. Twitter puts everything together, so

One commonality is that eberything you mentioned is a site that specifically gathers people around a common topic/interest. Twitter puts everything together, so the tweets from the hardware hackers I follow are mixed in together with joke accounts. This is one of my biggest pet peeves with all social media, I just don't understand why we haven't figured out anything better than usenet for keeping interests separated.