Why cheap customers cost more
For Appointment Reminder, approximate per-account customer support incidents per month.  I've taken the liberty of scaling them to X, where X represents the number for the highest publicly available account plan.  Personal ($9): 7X
  Professional ($29): 4X
  Small Business ($79): 3X
  Office ($199): X

The character of the questions is also different at the various plan levels.  Most common question for Office: "What's the timeframe on integrating this with ..." followed by "Our $TITLE would like a report saying $NEEDS, can you make that happen?"  Most common question for Personal: "How do I schedule appointments?" followed by "The system is working exactly the way it says it does on the screen.  Can you please tell me why that is happening?  I thought it would work in a way completely opposite to the way described on the screen.  It would be convenient if you could fix that.  No, I didn't read the 'If you want this to work in the opposite fashion...' text on the screen to change that setting, I have more important things to do than worry about computers."Your mileage may vary.  If I were doing the math based on phone calls waking me up in the middle of the night, the numbers get skewed due to one pathological customer in the $29 bucket, who has literally called me more than every other customer combined.P.S. I have fairly exact privileged information regarding this question at a handful of companies and anecdotal evidence from dozens of my software buddies.  It is our universal experience that the support load for cheap/free customers crushes the support load for the higher plans, both on an absolute and per-customer basis.