I believe it's been posted before, but sethbling (of vanilla-minecraft-hacks fame) pulled off the impossible and did the credit warp on an actual SNES, live[1]. As this video very-nicely explains, this required incredible amounts of pixel-perfect accuracy.
Lining up the line of koopa shells on exact x-offsets and very narrow heights mid jump (!) to write the landing-sled - using a controller, realtime - is utterly insane.
As a side note sethbling's latest project is teaching[2] (using neuro-evolution) his machine learning bot to play SMW[2], SMB1[3], and Mario Kart (original)[4]. While he machine learning is simple by today's standards, his brief videos give a really nice introduction to the topic that should be accessible to most people.
[1] https://www.youtube.com/watch?v=14wqBA5Q1yc
[2] https://www.youtube.com/watch?v=qv6UVOQ0F44