I never did have good tracking metrics in place for time spent per customer. I was a one-man shop and this was in 2000-2003, so there were limited open source options.
Customer support ate up a little more than half my time. This took away from programming and business development. Of the customer support time, maybe five or ten percent was spent on these ten customers -- and that is out of ten thousand paying customers and a few hundred thousand free users.
I never got a four million dollar phone call, but I also don't know how much these ten users evangelized my services. Who knows -- maybe they were responsible for a thousand paying customers?
There's an old phrase: "I know half of my ad dollars are wasted, but I don't know which half!" Nowadays it's a lot easier to measure return, but I still think we're not at the point where we can quantify good will from customer service.
You can always make sure that all your interactions are as pleasant as possible. That will cost you very little time and will leave a lasting impression.
Today I had my first (and hopefully only) encounter with Dreamhost customer support. I was trialling a setup for a client who was looking to host 3 sites with them. By no means a big account, maybe not worth their time. Because of the way I was treated I will have nothing further to do with them as a company if I can possibly help it. I will never use them myself and I will never recommend that my clients do either. Had they taken the time to offer me courteous support I could have gone away happy and the entire process could have been completed faster. Sometimes you don't even need to be nice, you just need to show some manners.