I'm not a big user of Twitter, barely at all.
But of all the social media I think Twitter is here to stay, and I hope I'm right about that.
Yeah there is a lot of fluff, and some will never get past that. But the fluff is just the filler in between instant and urgent news type stuff.
I also think incrediBILL's example of the customer support fits that instant and urgent model well.
In that light, I think the severe constraints on message size is a real plus, they're what I think will make the system continue to function for the benefit of the users overall.