"If you don't design a site from the ground up to be redundant and highly performing, its pretty difficult to flip a switch and make it that way later. Which is basically what Twitter has found out."

And really, that's OK.

Sites like Twitter are popping up precisely because the bar is very low to get your idea out on the 'net and compete. Sure, the cost in dollars and person hours is much higher to refactor for stability later, but would Twitter have even come into existence if that was a requirement from the start? Would its founders have considered it a worthwhile risk?

Jason