Twitter and Facebook are duking it out to own the future of the social Web, though users won't have noticed. Indeed, for those who use both, this may come as a surprise, since the two, while both social media platforms, seem to serve very different purposes.
Tell that to Twitter and Facebook, which increasingly have painted big bull's-eyes on each other.

They probably should spend more time painting their home pages. While the two Silicon Valley companies have opted to skirmish in the hinterlands of APIs and data feeds, the war will almost certainly be won somewhere else: user interface and ease of use.
Facebook groks this more than Twitter, which is why your mom/dad, teenage neighbors, and friends all use Facebook, and probably don't use Twitter.
Both companies have open APIs that encourage third-party developers to build out their respective platforms. Facebook has the Open Stream API; Twitter, the ">Open API Service.
These are critical components of a platform strategy, but they're secondary to the lesson that Microsoft and Apple have taught us: if users don't care about the front end of software/services, developers won't care about the back end of the same.
Facebook largely works because people know how and why to use it. Twitter...not so much.
It's telling that Twitter's "big" feature of the last six months is...lists. I use and love Twitter, but after a month I still can't get myself excited about creating or following Twitter lists. I'm not even sure why I'd want to do so.
Is this the best Twitter can do?
This is perhaps why Twitter seems to work for a narrow class of user: Caucasian, middle-aged urbanites with no kids.
In other words, not teens, not your mom/dad, and probably not you.
Facebook's demographics look very different, probably because its current range of uses is very different.
To me, this is a user-interface problem, and not a defect in the DNA of the Twitter platform. It's simply not immediately obvious what one should do with Twitter. That's not the case with Facebook.
We learned this long ago in open source. What separates a good but doomed project from a truly great project is documentation (to help developers know how to use the system) and user interface (to help end users know how to deploy the software). That's why Linux was interesting but not ubiquitous until Red Hat, IBM, and others added the finish that made its power usable by the general business world.
Twitter has a lot of promise, but not yet much polish.
It's nice that New York gangs have found new ways to dis each other using Twitter. It will be better when Twitter makes it easy and obvious for me to talk with my parents using Twitter.