Twitter's approach (atleast in the early stages) has been more of Darwinian evolution ("Shit, we have to do something about this or we're screwed") rather than

Twitter's approach (atleast in the early stages) has been more of Darwinian evolution ("Shit, we have to do something about this or we're screwed") rather than planned evolution :-). It has probably served them well -- the growth they saw in usage meant they could without thinking too much whether something was worth it, evolve to more sophisticated solutions as time went by.