Shira Ovide has a great interview with Dick Costolo in the Wall Street Journal.

Here's my favorite part:

WSJ: Intense investor interest in tech startups, including yours, means some young companies drew particularly high valuations. How can Twitter live up to high financial expectations?

Mr. Costolo: We want Twitter to be one of the lasting, remarkable companies. Revenue and profits are the fuel that will enable us to achieve what we feel like we have to achieve, but it's always in the context of why it's important to our users and the world, and not because we have to achieve a [certain] valuation.

We knew there was a significant [revenue] opportunity here, and we went out and proved it. We're not running around thumping our chests about it, but I think we all feel vindicated. We ignored the snickering.

WSJ: Does it matter if Twitter never has as many users as YouTube or Facebook ?

Mr. Costolo: I don't think about our goals in terms of other companies. Where we want to get to is human scale, global scale. That's a billion users, not where we are today. We're the size that 99.9% of the other companies would like to be, but we believe Twitter is valuable to everybody on the planet.

WSJ: How are you trying to narrow the gap between the large number of people who have heard about Twitter, and the smaller number who try it and stick with it?

Mr. Costolo: Once you become a core user, [Twitter] is indispensable. But you have to invest, frankly, too much to get that 'aha' moment. One of the things that we're spending a great deal of time on are weekly digest emails for casual users. It's a great way for people to start realizing, 'that's amazing and I need to be checking in more frequently.'

A lot of people still don't understand what Twitter is.

That's why it's so amazing that they're doing as well as they're doing.

There are still many people in my life who don't know why they'd ever want to use Twitter.

I just re-read the WSJ Dick Costolo interview.

TWITTER USES DIGEST EMAILS TO ENGAGE WITH USERS.

Email is about as far from real-time as it gets.

But it's essential of user engagement on the Internet.

And even Twitter must embrace it.

I think that's quite smart of Dick, actually.