This has to be one of my favorite stories about a Newgrounds contributor...
Back in October of 2003, Daniel Rocha (LisVender on NG) submitted his Flash video for the Weird Al song Angry White Boy Polka.
It turns out, Matt Groening's (creator of the Simpsons) son is a Newgrounds fan, and Matt showed the video to Weird Al during a Simpsons party at his house. Daniel was contacted by Al's drummer and manager, and soon found himself with back-stage passes for a Weird Al concert, where he got to meet Al and take some pictures!
The entire story will forever be documented in the history section. You can read Daniel's account first-hand! It's pretty inspiring to think about who might be watching your submissions!