A few months ago I had found an awesome hack for Super Mario World, called "Super Demo World: The Legend Continues" (see
this posting). Or just google for it, you should find it quite easily.
A few people had asked me to do a time-attack of this (finding all 120 exits), and as I was bored last weekend, I gave it a try. However this is more a walkthrough than a timeattack; I did not use any slow-down, and only used ~ 7000 rerecords for a playtime of almost 3 1/2 hours (YES, this game is very complex!!). I also didn't plan out any worldmap route, I just followed it in more or less chronological order. The general gameplay can be called fast but not perfect, in some places quite sloppy - I'm not really a great player :P The level routes are probably also improvable, however I did find some nice shortcuts which the programmers most likely did not intend :)
Overall I estimate a perfect timeattack would need something between 2 1/2 and 3 hours, but it would be loads of work to optimize it, and probably not worth it, as not so many people would watch it in the end...
Anyway, for the ones interested, you can download my movie
here
If you want, you can download some savegames
here, I saved after each completed world and made one last save before entering Big Boo's tower.
Enjoy :)