This Week in Startups interviewed the founder of Evernote founder, Phil Libin, who talked about the freemium model and why it is important to keep all his users, even the ones who don’t pay.

Host Jason Calacanis starts off by asking Libin about a dynamic in the web now that people are starting to pay for services that they feel is important to them.

Libin agrees, and structures his product to get people to love it and want to support it.

“It’s more important for us that you stay for life and never pay than if you leave, because chances are you are telling your friends about it, you are talking about it, and you are more likely to pay,” says Libin.

“The best way to get someone to pay is to make them feel that they never have to pay. Give them enough time to fall in love with the product and then they want to pay.”

Asked about his overall conversion rate, Libin says it is three percent, but he says the number is meaningless. The more important number is length of usage, since the longer someone uses the product, the more likely they are to pay. The people who have been with the product for 2 1/2 years have a conversion rate of 20%.

Libin says that has changed how he designs the product. He makes feature enhancements that will keep people engaged and loving the product. He doesn’t want to push out his cohort.

“Nine out of ten things we add are free.”

Evernote charges for services the company couldn’t provide economically for free, like services with large storage costs. The company also charges for services that would be particularly useful to power users and corporate users.