https://www.youtube.com/watch?v=YZwiQd-0xqQ [0] is Nick Yee's talk that he mentions in the first couple of minutes (that he says "destroyed his entire presentation").

http://www.gdcvault.com/play/1023242/The-Gamer-Motivation-Pr... is the GDC version, though I imagine they're exactly the same, with the slides at http://www.gdcvault.com/play/1022959/The-Gamer-Motivation-Pr...