I can't decide whether I agree with justbaseball or not. When a kid is a standout player (as his were), then yes, someone's going to notice you at a camp/showcase, whether that is the camp at the school he wants to attend, or a showcase with schools at the right level. The question many of us have is, if your son is not that kind of player, does that mean (a) you're not looking at the right level - very possible - or (b) you have to work harder at generating interest?
In my son's case, it varied a lot. A couple of schools did respond to his emails, and followed him during the summer. Some it was a combination of connections with his summer coaches and son's emails. He also got recruited after PBR and Headfirst by schools he had never contacted. Some of it has to do with whether you are looking locally or on a wider geographic scale (i.e. the local coaches might have heard of you through local networks); and, in hindsight, I do think that having your summer coaches contact schools is better than doing it yourself, if they are willing to do it (and have the connections or credibility).
I do agree with JBB that coaches know what they're looking for, and when they see it, they go after it, whether or not there was any prior contact. The question is, does prior contact help, at least in some cases?