Whittler, I agree that when a bow fails, usually the first question asked is "what kind of string was on it", and if it's a high performance material it often gets the blame. However, I have seen bows damaged by the string. Some failures are questionable, some there is no doubt. I also agree that HMPE materials aren't about speed/performance. The other benefits are so great that I'd use them if they were slower.
4runr, there's more to it than just how the string is made. The string definitely needs to be made correctly, but the string grooves on a "FF" rated bow are cut at an angle, and the tips reinforced. Every old bow I've looked at had the string grooves cut straight across, and that makes a difference.
I don't know how some folks get away with it and others don't. Guess it's like some folks who smoke and live to be 100, or some drive like a maniac and never get a speeding ticket...others aren't so lucky.
There definitely is a risk, and how much of a risk it is depends on a ton of variables.
For me, it's an easy solution. I don't have any bows I'm willing to risk it with, and even if I did I don't want to risk any knots on my head or splinters in my hand, so I only use HMPE materials on bows built for it.
Chad