[jshen]

It's not primarily about the size of traffic, but the ability or inability to cache. At work we serve a ton of traffic with MRI ruby and 3 small VMs. Most requests are served by varnish and never hit the ruby stack. Most people do a terrible job at caching (edit: I'm not saying that twitter is bad at caching).

[kayoone]

Twitter is hugely write intensive and needs realtime data, so their caching needs are probably vastly different from yours.

[jshen]

That was my point. Their caching needs are vastly different from almost everyone!

[bryanlarsen]

Agreed. I've got a page that takes 20 seconds to render on a dedicated fast machine. I could spend some time optimizing it, but even then it would still be slow. However, it's cacheable so I can fix performance problems with a simple post-deploy script. We can't do that for every page, but it's awesome when we can.