We do 400K+ users an day on our Rails app, 10MM pageviews, and 200 requests a second. YellowPages.com, which is probably the largest Rails site (yes larger tha

We do 400K+ users an day on our Rails app, 10MM pageviews, and 200 requests a second. YellowPages.com, which is probably the largest Rails site (yes larger than Twitter) does a lot more than that. I used to buy in to the whole 'scale later' philosophy from 37signals, but after getting burnt by a fast growing application and being down for half a month - capacity planning is definitely worth it over being caught with your pants down right when you're growing.