I have beat the original, though I never did beat it until after Mario All*stars came out (long after, as in 3 to 4 years, I think). I saw other people beat it, though. Does that count?
I have finished it with no warps, then with warps, then in multiple forms (small Mario, big Mario, fire Mario, Luigi..), and in multiple fashions (Nes, Super Nes, GBC, Gamecube, Wii).
.. and to keep up with the topic (or rather, the off topic): my screen name usually derives from what I am, or who my favorite character is (I am known as SuperMarioFan at GameFAQs, and Toad here, the only two forums that I visit).