A chat server? Yawn. And it's not for 70 million people at once, that's user base, not simultaneous logins.
AIM, Bonjour, Gadu-Gadu, Google Talk, GroupWise, ICQ, IRC, MSN, QQ, SILC, SIMPLE, SameTime, XMPP, Yahoo, this is a solved problem.
AIM, Bonjour, Gadu-Gadu, Google Talk, GroupWise, ICQ, IRC, MSN, QQ, SILC, SIMPLE, SameTime, XMPP, Yahoo, this is a solved problem.
As for the dark launch thing, it is a fancy trick, but there are ways of doing load testing in an automated system by having test servers simulate the load from real users. This usually can give you much better data without wasting bandwidth, slowing down users' experiences, etc.
They had a problem, they solved it in a very cool fashion using the best tool for the job (Erlang), they thought of a very good way of testing the application, and they were gracious enough to share their experiences with us, other developers...
Seems like a win all around, so I'm not going to complain.