lhpmom- if I remember correctly my son received an introductory letter from Stanford. He wrote back and then I think got a second letter with questionnaire, grade and transcript request. Sent that all back.
I think he then got a few other form letters and a camp invite. this was all back when he was a sophomore. He had other committments and didn't go to the camp after his soph year, but did send them a letter explaining why. Around December of his junior year he got a letter and camp invite and sent it in immediately. Got a few other letters until the summer camp and attended this summer '03.
Overall I think the camp is a must. The exposure you get to dozens of colleges is amazing and my son has been seriously recruited by several schools that saw him there and I believe (hope and pray) will be ending up at one of those schools. He's waiting to hear from the admissions office.
Best advice I could give, don't think of this as simply the Stanford camp. If Stanford wants you, they'll find you IMO. I think they might take 1 or 2 kids from the camp (if any) and they are typically high profile kids that were known in any event. I didn't see the camp as being about Stanford. It just happens to be held there.