How to build huge services?

[8623012]

Hi!

Recently, I'm interesting for thinking how to build huge services based on FreeBSD.

Like some ISPs or portal site, the number of customers may be more then ten million.
In the so big environment, how to plan their services?
For example, 
how to build mail system for more then ten million users?
(smtp + pop3 + imap + webmail, and each user has 50MBytes disk quota)
And how to build so monster size web hosting?


In my opinions, 
First, using dns and layer4 switch (ex: alteon) to balance the load.
But, there are many problems still exist, like storage, authorization, etc.
How to solve them?

sincerely,