Is MySQL Good Enough for Large Scale?

My question is probably fairly common, but I wanted to ask it anyway.

When choosing a database type for large scale application (social networking, for example), is MySQL able to handle it? I mean, hundreds of thousands, if not millions of users...

If not, I can't imagine that everyone would be using Microsoft Servers and SQL. What would be the suitable alternates?

Facebook uses MySql. See this video, a presentation by Facebook devs, on how they do it http://www.readwriteweb.com/hack/2010/11/facebook-mysql-scale.php

this is a list of a few big fishes that use MySQL:

United Nations
Mc Graw Hill
YouTube
Facebook
Adobe
Wikipedia
Wordpress
Drupal

I hope this could help you to clear your mind ;)