What a dumbass I am. I have a new Giant OCR3 composite, and have been adjusting the seat height a little each day trying to get it just right. Today, about half-way through my 25 mile ride, I was dying. My knees were killing me, my butt hurt, and I just could not get comfortable. I decided when I finished that I really needed to raise the seat some more. I looked at the post, and the seat had slipped down about 4 inches, I hadn't tightened it enough. I can't BELIEVE I rode that long and didn't figure it out.