First time was a long haul US Airways Flight (PHL->BRU) circa '09 or so. Can't remember the specific aircraft, but the seat was leather and almost fully reclined, but wasn't a lie flat. There was nothing preventing me from sliding forward and off of the seat as I tried to sleep in the "almost lying down" position.

I got off the plane and realized that I have actually gotten better sleep in coach on long haul flights by wedging myself between my seat, the seat in front of me, and the window than in Business/First Class. That's changed in the years of the lie-flat seats, of course.