I did this, it was easily the most terrifying thing I ever did. I was hungover so it's probably the only reason I made it off the ledge.
When I was there about 4-5 years ago, the guys that ran the platform were really funny. They had a list of rules of who couldn't jump. One was "being Canadian"
One guy was saying how it was his last day, and how he was having a hard time concentrating...lots of funny banter.
They also had a variety of ways you could jump. One of them they hang you from the platform horizontally and pull a release pin when you are ready. One of the girl's I was with chose this option, and the operator was like "ok, we'll go on 3. 1..."and pulled it out, she screamed the whole way down.
The only way I could do it was just to run straight off the platform. It took me a while to actually do it. The best part is that when I saw the video of it afterwards, I saw that my legs kept running in the air as I was falling.
Worst part...the shirt I bought was way too small, and I lost the DVD before I left NZ.
Did you do the Shotover Jet boat?