Another DIS thread taking on a life of its own! I have filled out FAFSA for 3 years now, but I do agree that many private schools do not require it for merit scholarships. Sometimes this is clearly spelled out on the website as - all applications are automatically considered for merit scholarships - and sometimes you have to ask. My DD's scholarship was awarded strictly on merit, and we filled out FAFSA to see if she could get some additional grant aid. Several private schools offered her merit money this way, heck the U of Pitt offered full tuition early in the fall, long before FAFSA was even available to be filed.
Next year my DS will be applying to a very selective program. The school has a list of test scores/GPA to qualify for a certain amount of scholarship aid. Since he will qualify for a partial scholarship, and not need FAFSA to get it, I will have him check the box that he will not be applying for financial aid, as I believe this will give him an edge in acceptance. Many privates are not need-blind in admissions.