I flew to the US last week and visited the flight deck once on the ground. Unfortunately in flight is an absolute no no and probably always will be. It was good enough to see it on the ground, the ground power hook-up fell out a couple of times so it's a good job the APU was still running.
Some engineer guy came up to look at some stuff while I chatted with one of the pilots. It was good of them to give me a few minutes after a ten hour flight, I was pretty tired and I didn't do any of the flying.