Google users, Coleman said, "have started to drive design on Labs features. A bunch of things we've launched have come out of those requests."
He points to Gmail's Advanced IMAP Controls, Mark as Read Button, and Canned Responses as features that began with user feedback.
Coleman said he didn't have any metrics to correlate the pace of innovation at Gmail with its rising usage, but he said the service is growing faster now that it did in the past.
According to comScore, Gmail had 26 million unique U.S. visitors in September 2008, up 39% from a year earlier. That's far better growth than either Microsoft or Yahoo saw during that period. Yahoo Mail, however, still has about four times as many users as Gmail.
Nonetheless, Coleman said Google's focus is more on the quality of users than the quantity. He said in general he would prefer to have the most passionate, active users.
Gmail's product design and development aims to make users happier, he explained. "We've found that investing in [user happiness] ends up triggering some kind of idea about how to make some kind of successful business out of that," he said.
Gmail, though Google Apps, now brings in revenue from those paying for Google Apps Premiere Edition. It also generates some ad revenue from text ads placed in the Gmail window. Coleman said that users accept the ads. "The feedback is that ads are not intrusive and occasionally useful," he said.