I was a stand-by with a lot of seniority. I know there were other stand-by's who were unable to get on. They definately got bumped because of a weight restriction. I have gotten on planes that were booked like 20/24 in first 178/158 in coach. I usually plan about 5-10% no-show factor. Higher for 6AM flights. I have almost mastered the art of flying stand-by, even with 90% loadfactors and busy travel seasons. But when a weight restriction gets thrown in the mix, I can get screwed.
Anyway, thanks for the responses.