The last player who did break through that barrier currently holds the NBA career record for free throw percentage. He retired in 1980. And he didn't have a bad jump shot, either. Food for thought.
I also watched this video: http://www.youtube.com/watch?v=V4eJSjwlD5o
One thing to keep in mind is that even though Rick Barry achieved a 90% percentage, who's to say that others could achieve the same? The 90% number gets touted a lot but the number is from a sample size of 1, and from a great player to boot. Shaq could have improved his free throw percentage, maybe by 10 to 20% but I doubt he'd ever get to 90%.
Anyways, I agree that any free throw shooter in the 40-60% range should adopt the technique if at least to try it out. It'll probably take years to perfect however.