[joshontheweb]

It is certainly possible. I started charging last November and am just passing this threshold without spending any money on marketing at all. This might not work in all cases though. I have a bit of an advantage in that my users are podcasters and they tend to be good promoters with built-in audiences of their own. Also, my service is just naturally viral. The hosts have new guest on their shows all of the time so new people are getting exposed to the product regularly. When they see the ease of use, many of the guests sign up themselves. Not sure how you would recreate this in another domain but hope that helps.