Feature for Twitter, Follow, and REALLY Follow.
Getting lots of followers on twitter by following lots of people works well enough, but increases the noise to where you miss stuff from those you really want know about. Let me create a REALLY Follow list that bubbles up tweets from these people to the top and hides everyone else's tweets further down on the page or on a completely different one. Like a priority inbox for Twitter. I've wanted this since very early on. Some of the best tweeters get drowned out. It says a lot that Twitter basically gave this power to advertisers (promoted tweets) for them to put themselves in front of us more visibly.