The mandatory service plan was the deal breaker that led to my cancellation. It was honestly more of a straw that broke the camels back thing for me though. When I placed my reservation, I knew that the only Model S I could afford was the 40 (and the only option I was planing to get was active air) When the real world range numbers for the 85 started coming out, I started having some concerns about weather the 40 would meet my needs, as I have a 90 mile commute 1 day a week. I was not 100% confident that the 40 kWh would have been sufficient for me in the long run once the pack starts to degrade, particularly on cold winter days. I had talked myself into the fact that I needed a 60, and while it was a major financial stretch, I thought I could make it work. When the mandatory service was announced, I ran the numbers, and realized that it would add $87.50 per month expenditure to my car (I drive 18,000 miles a year, so would need 1.5 service visits per year, and as the closet tesla store is 2 1/2 hour away from me, i would need ranger service. Since all available cash would have to go to the down payment on the car, and I would not be able to pre-pay, I would be paying $700 per service call. When all the math was run, it was $87.50 per month I would need to set aside) Now of cource, $87.50 is not much, but as I was already stretching way beyond the comfort level to go with the 60, it was simply a bridge to far. I ended up cancelling my reservation, and leasing a volt.
The sad thing is, If I knew then what I know now (that the service would become optional, and that the 40 is really a 60, and thus can use range mode without fear of degradation, and can be upgraded latter when funds allow) I would probably be driving a brand new 40 kWh Model S right now
I think most people who had a dealbreaker that made them cancel are in a similar situation. Its not just 1 little thing that made them cancel, but the combination of many things, with one item pushing it over the limit.
