I use both Twitter and Facebook, but in very different ways, and I get very different user experiences out of both of them. My Facebook friends list is very highly curated; although I sometimes feel bad about it, I have a fairly strict rule about only having people on my friends list that I actually know, in person, and are friends or close colleagues in some way -- not just people I met at a game dev conference somewhere. The reason for this is that I use Facebook for more personal updates and targeted discussion.
My Twitter feed, on the other hand, is a much looser, less committed stream of stuff. Unlike Facebook, there's no mutual requirement for following, so I'll tend to follow anyone who seems remotely interesting until they prove themselves not to be, at which point I'll remove them -- because, unlike Facebook, I feel less obligation to follow someone on Twitter since it's less personal.
The problem with both of these is that they're at opposite ends of the stream control spectrum. Facebook has always had algorithms that are out of our control as users that dictate which posts from which friends you see, and has implemented even more controversial stream-throttling mechanisms recently with their promoted posts. You're able to set up lists to offset this, but the effort to do so is high enough to be a bothersome user experience.
Twitter, on the other hand, has zero internal stream-throttling mechanisms. Again, like Facebook, you can set up lists to manage this, but it's to achieve the opposite experience from Facebook -- your feed can be so noisy that you need to set up lists so that you don't miss anything.
I do some management of my Twitter feed in order to make it useful rather than too noisy. But even with some pruning and management, there are posters I enjoy following who are just really, really prolific. And while I might enjoy many of their posts, I often wish I could throttle their post stream just a little bit, depending on who the poster is.
The type of throttling that I'm envisioning already exists in Google News. Google News allows you to list your favorite news sources, but then set a slider value according to how much of that source you want to see in your news feed -- "seldom" to "always", with values like "rarely" and "occasionally" in between.
I would love to see this kind of slider implemented on the profile of people I follow, and setting it controls how many posts I see from them in a given time in my stream.
What would the algorithm be for determining how to throttle a user's posts? Would it be time-based or content-based? I'm not immediately sure, but I imagine some basic UX research could be done with Twitter's users to determine what value they get out of the posters they follow or how they "use" their stream to find the answer.