[camus]

Github and the thousands of Rails powered websites have no problem scaling, so i'm pretty sure neither Ruby nor Rails are a problem.

[jacques_chester]

Github is an easier problem: generate pages.

Twitter has to deal with very high fanout and low cacheability.

[thebluesky]

With enough hardware you can make virtually anything scale, for a price...

[camus]

Well github is quite profitable , maybe that's twitter's problem... what service does twitter provides that people are willing to pay for ? None...

[elchief]

500 million users is more a little more demanding than 2 million users.