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>>How many users actually use your application?
last count, about 1.3 Million, cept all but 2 of them wouldn't know it.

>>How many users actually use your application?

Actual users is impossible to gauge, as a lot of what I write and wrote is used for B2B automated transactions so no human ever directly uses it.
The results of those transactions though influence millions every day, either directly or indirectly. From telephone bills created using data that software I wrote insert into the billing system to stock traders getting market information through software that calls webservices that call backend processes I create or maintain, hardly anyone directly uses my products but many do so indirectly.

And yes, I fully agree with the conclusion, that seeing something you created enter production and actually be used by customers directly or indirectly gives satisfaction.
I never had that during the 5 years as a consultant. Always coming in with the project half done and leaving again before it's complete gives you always something of an empty feeling (though you can have a lot of fun and learn rapidly).