One of many things I really enjoyed working as a Sales Engineer back at MySQL Ab and Sun was that I was paid full time to encourage companies to use open source for their database layer. While Linux has already become the norm for the operating system on servers, and open source alternatives exist for app servers, it wasn't until a few years ago we really started seeing major traction of that in the database layer. And I was happy to be a small part of it!
I'm not really a salesy person. I mean I'm good at evangelizing something I believe in, addressing customer business needs and such. But you couldn't get me to lift a finger just to meet a quota, if I didn't really believe in the product. Which is what good sales guys can do. (Also known as "selling what you have in the truck".)
But thinking back at my time selling MySQL, I felt it was a great privilege to be paid a salary to travel to companies around Europe and spend a day with them explaining how and why to migrate from a proprietary database they had standardized on, to MySQL. And btw, we always met our quota too.