Help a Scoble out. What should Robert ask in his scalability interview?

One of the cool things about Mr. Scoble is he doesn't pretend to know everything, which can be an deadly boring affliction in this field. In this case Robert is asking for help in an upcoming interview. Maybe we can help? Here's Robert's plight:

I’m really freaked out. I have one of the biggest interviews of my life coming up and I’m way under qualified to host it.

It’s on Thursday and it’s about Scalability and Performance of Web Services.

Look at who will be on. Matt Mullenweg, founder of Automattic, the company behind WordPress (and behind this blog). Paul Bucheit, one of the founders of FriendFeed and the creator of Gmail (he’s also the guy who gave Google the “don’t be evil” admonishion). Nat Brown, CTO of iLike, which got six million users on Facebook in about 10 days.

What would you ask?