i think the problem with twitter is that they did not use a real time architecture, like email, irc, or some other messaging platform. instead i think they write each page dynamically off of a db call based on who subscribed where. ie, you would have to start from scratch to scale it. i think the problem is that now that twitter, let the cat out of the bag, they are now chasing problems on an old architecture, and trying to scale that, while also trying to build a new version. it suppose its like running two tech companies.