I ran a website for a couple of years without thinking about turning it into a business. Finally, shortly before I graduated, I decided that I need to make money from it, otherwise I can't sustain it any more. Over the years, 30,000 people used my "startup" and in the end, I had a round 5,500 active users.
I thought a lot about the pricing model, but turning a free service into a paid one, is not easy and truth is, I'll never find out how it would perform with a different pricing model. So I just made a decision and tried it. I decided against freemium and started charging 1€ at the beginning of this year. The intention was to make it a no-brainer and convert as many users as possible. I converted about 50% of them. People pay either 6 or 12 months in advance (to lower the transaction costs).
My greatest fear was that there would be a lot of people who are not satisfied and want their money back or that I'll end up spending a lot of time on support emails.
Thruth is, from now 4,000 paying customers. I had exactly 1 person who wanted his money back. I receive about 2-5 emails per day, mostly telling me how great the service is and what kind of features they would like to see.
I literally spend 10 minutes per day on customer support.
Fact is, it depends on your business and something that doesn't get mentioned in the blog is that people don't care too much about a lousy dollar or euro per month to complain about something (some do, however, but rarely).