Amen to the most scouted event in Virginia. I can add it was the far and away favorite event my son ever attended among showcases, camps, tryouts, etc. The players get a little bit of the Rock Star treatment. No guarantees on playing in college, but it does guarantee exposure to tons of schools, and if your boy has a good three days, very hard to imagine he won't hear from a few folks.
You will hear that getting selected is a lot of politics. Our experience did not bear that out. Necessarily a lot of good players aren't selected, and I'd hate to be the guy that decides on the last 3-4 spots on any roster, but in our situation two local guys were invited to try out knowing next to nobody there (we're from the Valley, the tryouts were in northern Virginia), but both looked great on the field and were selected.
I'd estimate there were between 90-125 coaches present. Some Virginia schools had 2-3 coaches there, every ACC school, some SEC, etc. A very impressive show.