I love twitter.
I don't actually have a twitter or subscribe to it, but as a concept I think its brilliant/hilarious.
As far as it relates to this article by Zappen, its a wonderful example of constraints. These affordances and constraints set upon twitter users is what makes it so fantastic. Granted, there's some real crap on Twitter, but there's some gems as well.

You have a word count, a literal constraint on what you have to say. It is like a condensed, super charged version of of quotes and speeches. It must be direct, sharp, to the point and within word count. This makes the writer really think about word choice, meaning and delivery.
One of my favorite twitter writers, called The Captain, is a brutally honest, insanely witty person who chucks these sentence bombs out into cyberspace with the ferocity of a mother moose chasing a hiker.
There's not an excess word and everything is where it should be. You read his quotes and you innately want to agree/believe them because his rhetorical delivery is so strong and so fitted to the medium it is placed in.
I think constraints can actually cause a writer to flourish.
And in honor of twitter, I'm keeping this post short and to the point. There shall be no rattling on here.