A couple of recent 37signals mentions at Entrepreneur Magazine re: charging for products…

Harness the Power of ‘Freemium’

As for when a web service should start charging, Fried’s answer is simple: immediately. Charging from the outset tells users that the product has a specific value, Fried says. Trying to charge for something that was previously free can undermine the product’s value, causing potential customers to ask why the service is suddenly worth more than it was in the past.

“My feeling is that you should begin charging right from the start…The longer something is free, the less it’s worth,” he says…

“The best advice I can give regarding pricing is this: Have a price. Don’t be afraid to charge for your work. And make it a number you’d pay yourself,” he says.

Radicals and Visionaries

“You pay for everything in your life except some of the stuff on the internet,” Fried says. “That’s the built-in human behavior we’d like to mimic. The problem with this free thing is, if you’re going to hook people on free for four years, and all of a sudden start charging for things, that doesn’t work very well.”

Entrepreneurs are getting the wrong message from the Klondike buyout of YouTube and the “ridiculous” valuation of Facebook, [the founders of 37signals] say, pointing out both companies are still hemorrhaging cash and haven’t figured out a way to make money. Free is a bubble that will burst when investors run out of patience.

“I’ve been talking to startups, and people have this notion that all they need is eyeballs, all they need is a lot of users and then something magical will happen, and then they’re going to be a huge success,” says Heinemeier Hansson. “That’s going to lead to a lot of unavoidable failures.”…

“The answer,” Fried says, “is to be fair on prices, deliver great services that your competitor can’t and simply outlast free.”  

DHH and JF