John,
I've camped, hiked and climbed San Jacinto many times over the years in all seasons, and have never had altitude problems on San Jacinto. I've also had my entire family camping on San Jacinto, and my children and wife had no altitude problems, either. By the way, San Jacinto is only 10,804 feet. (San Gorgonio is 11,490 feet. And as with San Jacinto, I have had no altitude effects.)
On Mt. Whitney, it is a different story. Without acclimation, I really feel the altitude by the time I reach Trail Crest at 13,600 feet, and it seems most other hikers who are susceptible to altitude problems have similar experiences. However, since I know I have altitude issues, I am able to keep the problem in check and have relatively pain/misery-free climbs.
