Does anyone know what happened to Jamie?
He flew back to his home-planet ;)
Joking aside, i think Adam said he's back at work in his shop doing modelmaking/prototyping (not sure what he does exactly).
Adam said that once Mythbusters ended, Jamie decided that 13 or so years in front of the camera was enough. He never did enjoy having to slow down and work in a way that made sense on camera, so he also ended his fairly limited engagement with Tested.
That way he could work at his own pace on projects he chose entirely himself, or just enjoy some downtime when he felt like it.