I, sadly, had the occasion yesterday to send in my 10D for shutter lock repair. It wasn't caused by overvoltage equip. bcz I don't exceed the 6V Canon limit. However, in talking with Canon and further research, I found this from Chuck Westphal on another forum:
...as Chuck Westfall (USA Canon technical information director) puts it, the damage pattern is described more statistically: (speaking of the 10D at the time) nearly 100 percent of samples will be perfectly safe at 6 volts or below; Nearly 100 percent of samples will be damaged at 12 volts or above; between 6 volts and 12 volts, the percentage will vary, with failures increasing as the voltage increases. So just because John Doe's 300D works perfectly well with a 12 volt flash unit, it doesn't mean yours will--the odds are still against you.
This clearly indicates (to me anyway), further proof that Canon was not bound by, or at least didn't adhere to any ISO standard of 24V trigger voltage as someone else insisted. The statement that "nearly 100% will be damaged at 12V" says it all.
I'm not trying to re-open any sore topics, just bringing info from Canon's own USA Tech Rep about the 10D - simply for informational use of those who use a 10D and have any concerns about trigger voltage. I'm glad I didn't void my warranty. Others are certainly free to do as they wish and heed/ignore this statistical information.