My cousins went there. Two of them are there now.
I'm biased because I went to Hereford (graduated last year, now a plebe at West Point) and did very well by the public school system.
MDS *was* a very spiritual school, but I've heard one of the newer headmistresses isn't quite as spiritual as one in the past. It's physically beautiful, tries to mandate Mass, but the commute is killer.
Basically, it's a decent school. Kids are decent (though I'm sure my cousins could tell you some stories), despite the normal b**chery that goes on between girls. I think you can get a more in-depth education in the public school system, what with more AP classes. But then, I got lucky.
Thanks. That's the best recommendation I could possibly get. (I live in PG County, so public schools are simply not an option...and if you suggest moving, the additional mortgage payments are more than what tuition would be)
Best of luck at West Point!