Ask HN: Technical Sales Engineer

I'm interested in finding out if any HNers have ever been (or are currently) a technical sales engineer for a technology company operating in the (broad) IT space?

I'm specifically interested in your experience transitioning out from behind the monitor to a customer facing role. What were the challenges you faced? Do you have any advice for those considering making a similar move?

If you consider yourself an introvert it would be especially interesting to me to hear how you learned to step outside your comfort zone into an extroverted role.