"I think that's the number one reason why Mint is at the evolution that it's at, because we've paid attention to user-centric design," Patzer said.

Phishers, take note: Patzer said that good design helps convince new users to feel safe about entering sensitive information. "Design is also crucial to conveying trust," he said. "This is a personal finance service. You enter your bank usernames and passwords through this site. Trust is not conveyed through copy or the words that you use, it's conveyed in an instant through the quality of your design."

Patzer had little patience for sites that use made-up words, which are often hard to spell and hard to remember. He criticized and for choosing difficult names. "That kills your word of mouth marketing," he said, adding that Mint had not spent anything on marketing. The popularity of the site is due to word-of-mouth referrals, as well as Patzer's willingness to speak with practically any media outlet. He claims that he spends 30% to 40% of his time on press, because extra coverage can lead to special opportunities that otherwise would never happen.