Thank you for the compliment, keith!
From what I've been told and from what I've observed, there are not really any long term effects on your voice from doing this type of vocal, as long as you're doing it right. For instance Randy Blythe from the band Lamb of God has been doing this for about 15 years, and he only seems to get better. There are many other artists who have been doing this for an even longer time than him.
I think the people who lose their voices are simply doing it incorrectly. I feel no pain or any discomfort from this.
Thanks:D