I have. I have managed systems that handle millions of clicks a day in databases and billions of dynamic (PHP) pageviews on a daily basis.

I am currently managing a system that serves over 100,000 DNS queries per second, each of which is dynamically evaluated as to how we respond to it. And each of which is logged, amounting to over 7,000,000,000 log lines a day, all which get processed, parsed and in many cases handed over to a database store. Yep, we're dealing with BILLIONS of rows of MySQL per day.